I was fondling and humping at 12 years olds, probably much younger if I can recall. Probably 10. I remember, me and my moms boyfriends daughter used to have a bunkbed. I was on the bottom, her on the top. When my mom and her boyfriend used to switch the lights off, we would wait for them until we started hearing "snoring" in there room.
We'd already make a "time" or schedule to meet in the middle of the room LOL. So we'd check our watches, get up and meet in the middle, with the lights off. So we would have to search for eachother naked. From there, we'd just fondle and kiss eachother. I remember I attempted to put my willy in her, obviously at these young ages I didn't even know my foreskin could pull down so much. I remember it pulled and I squeamed like a little bytch LOL. We used to reenact sexual scenes in Movies too, Doctors & Nurses and I remmeber different occasions in Primary School where I used to run behind cafeterias with different girls and we'd just fondle and sucked on a few titties.
I was a horny little snotnosed 10-12 year old.
So, in a nutshell I was sexually active around 10-12. Had my first REAL kiss or snog at 14. Started having vigourous sex at 15 with my High School girlfriend. Had my first BJ at 15 or 16. Accidently got a girl pregnant at 20.
It doesn't matter if you started out sexually when you were 12 or more. I'd be more concernced about learning an instrument or sport at that age than if I wanted to get good at the former and latter in my late twenties. Really, it doesn't make a difference dude.