We started with Holmes box D&D, with the AD&D Monster Manual for monsters (I don't think the PHB had been released, or at least at age 12 we hadn't sourced it yet). I know by high school I owned the Traveller LBBs; but I don't recall ever actually playing it in a group - but do remember having a ton of lonely fun making sectors and ships. Then I took a break during college (wasted years, in multiple senses of the word "wasted). When I got back into gaming working at a comic shop in the early 90's, it was pretty quick that we tried other games. It might have been 1e Shadowrun. So maybe I'll land on 15 years or so? depends on whether we consider that lonely fun to be "trying another game"