I’m agnostic. I believed when I was younger, but then I found out it’s all a pack of lies. Nobody knows whether a god of any kind exists or not.
I was informed that there was a God, and accepted it as fact until I realised things didn’t add up. But I don’t count that as believing.
I can recall being very confused by Church shenanigans when very young, and a lot of the Biblical stuff just seeming very mythological. I wasn’t articulate enough to really understand any of those doubts, or brave enough to confront and question anyone in authority, but by age 11 I know I was well on the way to being an Atheist and haven’t really looked back since.
I was raised in a mildly religious family. I started questioning everything in my teen years and was atheist for awhile. I guess now I’m a spiritual agnostic. I think certain aspects of spirituality are important (morality, community, a sense of wonder and meaning and purpose, peak experiences) and certain aspects of religion are dumb (literalism, dogma, prejudice, violence). I’m agnostic about the supernatural aspects.
I’ve always been a natural skeptic. And just didn’t buy many of the biblical stories that don’t make much sense. And of course, the whole concept that a “loving God” will send you to Hell for not believing in him without direct evidence, doesn’t make any sense.
I can’t say there is no god. . . but, I have trouble believing humans are divine and live forever.
I was brought up Catholic for the first eight or so years of my life. I suppose I believed in god at that time (because I was told to) but I never really bought it. The rituals were pretty cool though. I always got C- in Christian Doctrine in school but got good grades in all my other classes. In fourth grade I switched to public school and stopped going to church. When I was a teenager I knew I didn’t believe but really didn’t give it a lot of thought.
I’m an atheist that once believed.
My dad and his whole family was Catholic. My mom and her whole family were Methodist. We didn’t go very often, but when we did, my dad went to his church and I went with my mom to her church. At least most of the time, it worked out like that. But I did end up going to a lot of Catholic masses over the years as well.
When I was a teen, I realized that the Catholic interpretation of the Bible was different than the Methodist interpretation. A friend of mine was also starting to doubt and we would talk a lot about it. From there it fairly quick trip to agnosticism then to atheism.
Same process for me, forced to go to church/Sunday school against my will as a young child, couldn’t believe even then, too many logical fallacies and plot holes
Fought tooth and nail to not go to church every Sunday, dragged against my will, used the time to daydream and ignore the indoctrination attempts.
By my teen years I flat just stopped going and never went back
Spent most of the rest of my life as an apatheist, didn’t believe and didn’t care, either, leave me alone, I’ll leave you alone
Now, I’m a hard line Atheist/Anti-Theist, and even better, my nephew and niece (12 and 10) have become atheists themselves 
My nephew even openly scoffs religious beliefs and makes fun of televised religious dribblings
I’m an atheist now. I grew up as a Methodist in a non-religious family (believed, but made no overtures) in a culture (Upper Appalachia) that assumed, rather than believed.
I never really did believe in the God that I paid service to. I went to Sunday School, Bible School, even became a “Lay Witness” as a teenager, but the truth was that I only mouthed the words, played the parts. It always just seemed like a Big Empty there where God/Jesus was supposed to be.
I was so relieved in college to find out that I didn’t have to keep up the act.
I was raised Christian so I guess I believed when I was a kid, but even very young I never really felt that it “took.” I didn’t get anything out of going to church, reading the Bible, or doing any of the other things that Christians were supposed to get something out of.
It took me a long time to admit it to myself (childhood indoctrination goes deep, and my family wasn’t even particularly hardcore religious), but I felt a lot better when I finally did. I’d say I’m more of an agnostic than an atheist, but I no longer consider myself a Christian.
I used to be an atheist as a little kid although it was more due to being it a “default” position rather than any reasoning on my part.
My parents were of the “Some believe X, some believe Y, and it’s important to decide for yourself” school, so I started out with “I don’t know about God(s) yet”, and, through the gradual increase of knowledge, eventually got to “there’s almost definitely no God(s)”.
By my preferred definition (‘expressing no belief in a God or Gods’), both positions are Atheist, so I guess I’ve always been one of those.