Started around summer, aught two. Although that's just with publicly sold games (i.e.: D&D) for the masses.
I can remember playing a game my friends an I simply called "Quest" as far back as in 5th grade. If I were to count that, then I really would be 15-16 years. It was a sort of diceless RPG we played. Quest had a Game Master-Player setup and we even used miniatures! I can remember drawing weapons and armor (swords, axes, shields, etc) on a piece of notebook paper as if they were hanging on a wall of a merchant's shop with prices under them.