Well I included the 12 and under to be comprehensive--certainly there are some 10-12 year olds trolling this forum ;-)
I've always been interested in the demographics of gamers (I'm 34, btw). It seems that there are general patterns that most (but not all) follow: get into the game sometime in childhood, get out sometime in late college/post-college years due to emphasis on grad school, career, family, social life, etc; some, maybe half, never return, half return in late 20s or early 30s when life stabilizes some.
I am always surprised at how, it seems, such a large portion of gamers are in their 30s and 40s--people (like myself) that got into gaming in the early years--late 70s and early 80s--and never got out, or came back. There are, of course, new gamers that "join the club," but it seems the bulk remains those 25-50, who started in the pre-White Wolf Era.