First kiss: It took about 3 hours of talking and hugging on her chilly back porch before I got up the nerve to kiss her. And it stopped at a kiss. She could been more aggressive, as she was older, but…
Ten years later, after army and college. Met a cute girl…“Wanna fuck?” “Why not?”
How times change.
I reached second, third and home, plus a field goal and birdie putt for good measure, all on the same night. So yeah, that was pretty memorable.
Man, you’d think you’d remember your first hand-on-boob at least until you had your second hand-on-boob experience, Bricker.
Just kidding. 
I’m 24. I know who the girl was (largely since all three of these were the same girl, albeit at different times), but I don’t remember a thing about the exact situation. Now that I think about it, I remember the other two experiences as clearly as day. Weird.
I’m winning, sweet!
I think.
63, and I remember it all as if it were yesterday–name, place, time, cup size…
But, strangely, I can’t remember what I did yesterday. 
On the bus, about 11pm, on the way home from DCI. Band geeks get all the action I was 17.
St. Luke’s Hospital.
I was 15.
Minutes.
I was 16. I remember his name. His face. Everything. I remember my first orgasm too, we were “exploring” not having sex or anything. When it happened I got scared, ran out of his living room and straight home. Think I hid in my bedroom for a couple hours.
Like Aesiron and Diogenes, first boob was minutes before first getting laid. Unlike Dio, I lasted quite a bit longer than fourteen seconds. 
ETA: N-n-n-n-nineteen.
I was also 13, a freshman in high school, and he was a freshman in college. We made out in the bathroom of my high school after speech team practice (he was another person’s coach, not mine). Ew!
And reading this thread makes me want to lock up my 15 year old son, just so’s you all know.
In the woods, about a month after I started dating my first girlfriend, when I was 13. Before me, she had been dumped by my friend and basketball teammate TJ, because she would not let him get to second. I have always meant to thank him for that.
Good Lord, you Westerners are early bloomers. 
I know tons of girls back home who are in their mid-20s and haven’t even been to first base, much less second.
Didn’t you go to a pretty conservative Catholic high school, though?
ETA: And I certainly don’t consider myself early (almost 18,) but yeah, the 13, 14, and 15’s seem pretty early.
Do I remember my first hand on naked boob? HELL YES!
I was thirteen. Her name was Lori. It is the only Bar Mitzva present I still remember.
I was 23, for what it’s worth, and now I’ve got a kid on the way only a few years later. I kinda wish I could take it all back.
Appreciate the definition in the OP — those “bases” being defined differently by different people & all.
Kelli, she 13 and me 15, her idea, in part if I am to believe my younger sister about subsquent conversations (and I have reason to), “your brother’s so weird, I wanted to see if he’s like other guys or not”.
Oh, and third base, too.
Collette, 16, in my car. It was fall, with a chill in the air, but that isn’t why I was shivering.
Like a cad, I dumped her the next day. I realized that she was nuts: clinging and possessive, and I wasn’t ready for a life partner yet. That took another year, and another girl.
I went to a private high school in Korea - the majority of my peers didn’t even start dating until college. Probably because dating was forbidden, according to school regulations.
I was 17. Cindy, in my parents’s car, parked along the river – first boob gropage, first bare boob gropage, first “girl’s hand on my cock-age,” but not to - ahem - completion. Sweet girl, great body, not a big thinker. I google her name every once in a while, but I’ve never found her.