In Junior High, got into my first serious group, we played in the basement of the public library every Saturday. That's how I discovered other games outside of the Dungeons and Dragons brand (first TOP SECRET, then STAR FRONTIERS, GANGBUSTERS, VILLAINS AND VIGILANTES, MIDDLE EARTH RP and ROLEMASTER, and gods know what else.) Started running games during then, too, mostly for 1-2 players at a time, usually friends from school. Got serious about being a GM in late junior high/early high school.
In high school, got into Marvel Super Heroes, DC Heroes, Champions, amongst others. Early 90's brought along Shadowrun and Vampire (and the rest of the WoD.)