I made the mistake of asking about the “other gods” in the ten commandments.
I was about eleven, and the Sunday School teacher had no idea how to answer it.
I was sent to the pastor, who told me that if I kept asking questions like that I would never be happy in life.
He was very very wrong.
While I was a young kid, my parents were sort of not terribly involved in religion-- they weren’t themselves atheist, but they weren’t practicing anything and weren’t bothering educating us in anything, other than Christmas carols (Santa and the traditional Judeo-Christian God were pretty well completely conflated for me). So in first or second grade was the first time I was really confronted with it through other kids who had this “God” thing going on, from whom I learned that I was this “atheist” thing. Which I accepted just fine.
Then there was the 'there’s no Santa (=no God)" moment at 9 or so that supported this, but then a conflicting time period in which I was sent off to church and tried to believe but always felt pretty well inadequate in my faith, and by 12 or 13 had whipped back to my default atheism by default and lack of training.
I never really became atheistic. I became more or less an agnostic omnist (syncretist? Whichever makes me sound more like a confused and apologetic douche ;)) at around the age of 14 or so. My father is not particularly religious, but my mother is a very active Christian with a syncretic tendency. I remember asking her how a just and loving God could punish otherwise caring, loving, and righteous Hindus, Muslims, or Buddhists simply because they put their faith in a different religion. My mother agreed and said that he probably didn’t and that most all religions are all working to more or less similar goals so they could all be valid paths to spiritual fulfillment. Lots of Christians (as well as fervent followers of other religions) will decry this kind of thinking, but it works for me.
Third grade.
I remember the day and the place and the time.
I simply “figured it out.”
I wasn’t upset at all. I wasn’t relieved. Nothing. No emotion. It was just as if I had finally understood the phases of the moon or why grass is green.
I grew up Babtist. Quite frankly that priest who would make the sermon every Sunday morning would scare the hell out of me. I was pretty convinced that my (or anyone’s) chances of getting into heaven were slim to none.
I’ve always doubted his existance but angry preacher man convinced me I should at least try and believe in God just out of the fear of burning in Hell.
I think I did this all the way until 3rd or 4th grade when we started to study Greek mythology in school. I remember thinking to myself how silly people must have been for believing such nosense… It was at that point a lightbulb went off in my head and I thought to myself. “Ya’ know what? I’m no different. I think I’ll stop the charade now”
I think it may have took a couple of more years for me to have the balls and just out right say I was an Atheist but that was definately a turning poit.
I think I might have been aware of the word atheist–I mean, I was widely read and a fairly intelligent child so I probably came across it a few times. But I was basically always taught that there weren’t any real atheists. Just people who turned their back on God. People who are angry at God. At no point was there ever a “people who simply don’t believe that God exists” option. I didn’t realize those atheists existed until I found the SDMB.
Some of my earliest memories I recall arguing with my mother over the existence of Santa. I wasn’t buying it. I couldn’t buy Jesus any more that I could Santa. I am simply not wired to be a believer. I never was. Throughout childhood I was very resistant regarding church and Sunday school attendance. Despite my early victory regarding Santa this would be a battle I couldn’t win.
As I grew older I began to wonder about some of the congregants. Among them were respected community members, the local mechanic, a bartender, businessmen who wore three-piece suits, teachers, and farmers. What were they all doing here? Did they really believe all of this nonsense? I couldn’t figure out why they volunteered to go through these absurd motions week after every loving week. I was not able to conceive a reality in which I was the only person who realized this was nothing more than an elaborate joke.
There was a time I did my best to believe in God, or at least appear that I did. I was given some responsibilities within the church as I got older. As a teenager I even entertained thoughts of attending seminary. That had more to do with wanting to emulate my pastor than any sort of calling. I had fallen into the routine and began to enjoy it to some extent.
After I had finally been confirmed my mother asked me if I wanted to continue attending church. I gave it some thought. I had been finally made a full-fledged member of the congregation which took more than a little work. All of these years it was all at my mother’s insistence. She was now simply giving me a choice. In the end I decided that I would rather spend Sunday being a teenager and getting into trouble with my friends than be a Lutheran. It turned out that I had made the decision to quit attending for my entire family. We simply quit going.
The last I attended a Lutheran service was in 1995 when my grandmother died. Twisting the dial on the radio one recent Sunday morning I came across a Lutheran church service being broadcast live. The rush of feelings and memories that it brought back were palpable. But it wasn’t a feeling of rapture, just nostalgia. Every detail of that old village church is burned in my memory from the smell of the pews to the way the hymnals were more worn on certain pages.
There is a big Lutheran congregation in a grand old church two blocks from my apartment. I’m considering joining. Were I to go back I would be one of those guys that a young version of myself would look at and think, “Really? That guy? Does he really buy this stuff?” If I did go back it would be to socialize, network and to be part of something. Do I buy any of it. No. But I can see why people do.
Freshman year of high school in history class the teacher was talking about how some people believe the Bible is literally true. I don’t recall really thinking about it all that much beforehand. My father is Christian, but my siblings and I were not raised in a religious setting. So I asked some questions about the flood, thought to myself “what a crock of shit”, and was sure religion was a lie since.
I’m not sure when I first learned about atheism, but my earliest memory of it is from when I was 11 or 12 and in the Boy Scouts. Our Senior Patrol Leader was joking about the fact that he technically wasn’t allowed to be a Scout because he was an atheist. This was around the time of the scandal surrounding the Boy Scouts excluding gays, when they were justifying it by claiming they were a religious organization.
I was raised a Catholic, attended mass every week, went to Catholic school through middle school, and was confirmed in the 8th grade. It was sometime in middle school that I began to assert, in my mind, that I did not believe in God. The truth was that I did believe in God, but denying him was my way of spiting him because I was unhappy with my life. At some point I realized that I really didn’t believe in God, and I began to see the absurdity of Christianity and other theologies. I started refusing communion at mass, and eventually stopped going altogether. This became an ongoing battle with my mother but she ultimately relented. To this day it’s still mildly awkward during Thanksgiving and other gatherings when I’m the only person in my extended family who stays silent during prayer before eating.
As some other posters have mentioned, it really was like realizing that Santa wasn’t real. It simply became obvious to me once I reached a certain age.
I was required to attend Sunday School at the local Anglican church from the age of 6 or so. My mother and other family members had no such imposition placed upon them.
After many weeks of mindless hymn-singing, group hand-holding and pasting stickers into books depicting how much Jesus loves us, I came home one day to declare that it was all a crock of shit.
Mum asked me why it had taken me so long to figure it out. 
I was in grade four or so.
All around the same time, I realized a few things.
First, that Adam and Eve had three sons and no daughters and nobody had a satisfactory explanation for how the rest of the human race occurred.
Second, I was told animals don’t have souls and don’t go to Heaven. Not even dogs. And when I asked why, I was told “that’s what the Catholic Church believes” and thought "well “I don’t believe that” … and that was when I sort of realized that I didn’t really believe most of it and that I didn’t have to believe everything my parents and teachers told me because some of it was very clearly untrue.
The final straw was in sixth grade when there was a discussion in class about how people who have had the opportunity to know Jesus and who aren’t Catholic go to Hell regardless of how good they are as people. I thought that was ridiculous, especially because everybody in every religion thought that they were right and there was no way to know which religion was “true.”
It wasn’t atheism for me at first (“atheist” was kind of a dirty work in Catholic school anyway) … I decided at first that I was a Wiccan, told my similarly-inclined friend that I had found a much, much more interesting religion, and experimented with it. Then I found a particularly ridiculous “spell” addressed to a clearly made-up “goddess” and realized that a lot of the stuff I had been reading is just stuff someone came up with and that, while parts of paganism made a whole lot more sense to me than Catholicism, I didn’t really believe it and the fact that I was using it as a game more than a religion was disrespectful to those who actually believed in it.
Somehow, even though I most certainly didn’t believe in God by grade 8, it took me longer to realize that some of the things that DA CHURCH says are horribly wrong and most of their political leanings made no sense and that was not where my heart was. Like on abortion and premarital sex… the whole “babykillers versus good people” thing got to me and I believed it until I was old enough that my friends started getting pregnant and the reality of it hit me. And I still vaguely intend to not have sex before I’m married, although I don’t really have a solid reason why.
I must have heard the word before I was 12, because I remember getting the joke in Once Bitten when they tried to use a cross against the vamp and she said, sorry, she was an atheist. 
I rejected religion piecemeal: first strict Catholicism, then cafeteria Catholicism, then Christianity, then religion in general. But I still had a vague belief in some kind of god, until I got into investigating urban legends. There was a certain amount of cross-pollination between skeptic sites and atheist sites, and I finally had to admit that applying the same scrutiny to the god question that I was to everything else meant I was an atheist.
Having had a long journey out of pretty heavy-duty religion, it’s weird to me that my kid is experiencing almost the opposite. She’s never been exposed to much in the way of religion, and as she gets older, we’re slowly explaining what this is all about. Yesterday she asked whether we celebrate Christmas and I said, “Yes and no.” This led to explaining that some people believe that baby Jesus came to save everyone from hell, but Mommy and Daddy don’t believe that. Her response: “So, those other people are wrong.” (Which was followed by some cultural sensitivity education.)
I’m not sure that I ever believed in god. When I was very young I didn’t understand any of the Latin mass but I loved the sound of it, I loved candles and incense and stained glass and pretty white dresses, Christmas and Easter and choirs singing hymns. To me, that was what being Catholic was about and god was a vague concept that I didn’t think much about.
I went to Catholic school and in first grade they start that ‘God is watching you all the time’ stuff and it was creepy. I remember wondering if he was watching me in the bathroom too and feeling scared. Then they got to the story of Abraham and how God told him to kill his son and I panicked. I was certain that if I was bad that God would make my father kill me and I was in hysterics for days. The whole 'Jesus loves the little children but his father will smite your ass if you act up" was terrifying at that age. I never got a reassuring answer from my parents or the nuns and it was too much for me to take. I decided that God couldn’t be real and that it was just one more story like Santa or the Easter bunny that adults told us about but weren’t real. I knew that I would get in big trouble if I said it so I never did, but after that I didn’t believe any of it.
That was me. In my country public schools are pretty much a waste of time so i was sent to a catholic private school since kindergarten even though dad is an atheist and mom is at best a not practicing catholic and i don’t ever recall a time when it didn’t feel utterly ridiculous to me, but i had to pretend not to get kicked out. I was baptised and had my first communion and was forced to go to church for some school functions but it was always just going through the motions for the sake of getting a decent education. The nuns who ran the place in my mind didn’t seem like any better people than my parents for all their faith.
I think I never believed in god, as far as I can remember. I used to go through the motions during festivals just for my mothers sake. But I stopped when I was around 14 years old.
Funny story. I used to make stained glass as a hobby, usually christian themed, and most people who knew me because of it were surprised to learn that I was not christian. I didn’t disappoint them further by telling them I was an atheist.
Agnostic, but close enough.
I wasn’t raised with religion, so I never gave it much thought. I remember clearly in second grade, someone asked me if I believed in god. I said “yes,” since that seemed to be the thing to do. But that’s when I realized “Hmmmm, I guess I don’t.”
Me, right around the “seriously starting do doubt Santa Claus” age:
M = me
P = parent
M: How did God get created?
P: God was not created. God has always been.
M: That doesn’t make sense! There always has to be a time before!
P: Not God. No matter how far back you go, God was always already there.
M: But couldn’t, maybe some space aliens have laid an egg and it hatched and that was God?
P: Then who created the space aliens?
M: <pauses> Older, different things in space. From before.
P: Then something would have had to have created them, too, see?
M: But that’s what I mean about God!
Can’t remember ever not being an atheist. Even long before I knew the word. As far back as I can think (which is probably around age 4 or 5), going to temple (I’m a Jewish Atheist, you see! :D) was a nice social/cultural activity, but this God dude has got to be some kind of Fairy Tale, like Peter Pan, or the Tooth Fairy, yes? (Yeah, I never believed in her, either – didn’t stop me from putting my fallen teeth where I’d get some money for them, though! ;))
I don’t really know, but I suspect both my parents and all my grandparents were/are somewhere on the very weakly deist – Agnostic – Atheist spectrum. Certainly I’ve never had any problem proclaiming that God doesn’t exist.
It’s probably our shrill, humorless female neighbor who was a vegetarian, wore black turtlenecks and a pageboy haircut, and generally seemed to have a scolding attitude toward the universe.
Put me right off of atheism and vegetarianism permanently.
Bad universe! Bad, naughty universe! You should be ashamed of yourself!