I remember very vividly being introduced to D&D at the age of 12. A friend of mine from junior high, Travis Dudley, had all five 1st edition boxed sets. Our first coupld of days with them were mostly creating level 55 characters and fighting Dragons. Not high art, but incredibly fun.
A year later 2nd Edition came out, and we started being interested in things besides just battles with dragons. I remember getting issues of Dungeon Magazine, and DMing adventures out of there. D&D lead off into other RPGs, like the teenage mutant ninja turtles universe, shadow runner, cyberpunk, and a range of table top games. It even lead to my friend Chris and I writing our own table top game (85 page rule book), that had 3 generations of game play mechanics at the age of 15. Yes, at 15 we spent our spare hours writing an 85 page rule book, printing out drafts on my dot matrix printer (which took about 3 hrs), and doing play testing and editing.
But it all started with cracking open Gygax’s D&D and a realization: with a few well crafted rules your imagination can take you to places you never imagined.