Wow, I'm the first person to choose young adult 20-29. I'm surprised.
But I guess it might be because I never had a moment where I actually said "I want to be a gamer." I've liked video games since I was 5 or 6 and first played my friend's NES. But I was only ever into one game at a time for most of my life. I played Heretic on my computer in the mid 90s. I played Sonic before that on my Genesis, and in the late 90s I played the absolute shit out of Goldeneye on another friend's N64. Even when I got a Playstation and then a PS2 a couple years later, I never played that much.
I've always liked them a lot, but I never became a gamer until I moved out of my parent's house and got a PS3. I didn't know jack about video game culture, and I didn't spend any time on gamer websites. I never watched trailers, never made walkthroughs, never argued on forums, never read fanfiction (well, maybe a little) before about 2 1/2 years ago. Then I moved in with my friend, who has a PS3, and played BioShock, and it wasn't long until I started acting like an actual gamer. Around then was when I discovered The Escapist, and I lurked here for a while before signing up an account of my own, for the interacting with of fellow gamers.
So, I'm still surprised that everyone else voting here became a quote/unquote "gamer" before I did. I feel a little old now...