So many ways to answer this question....
My older brother and I collected toy cars (the old Matchbox ones), and when we were playing with them, we'd also make up the names of the drivers, and stories about them and what they were doing. At one point, we even created some racing rules. That would've been around 1978 or so.
Christmas of 1980, I got D&D, and my love affair with paper RPGs began (it's still going). I was still in elementary school at the time.
In 1989, during my first year of college, I was exposed to play-by-email RPGs. In 1990, my first MUD. By 1993, I was a coder on an LPmud (SWmud, which is still in existence), and had run multiple RPGs via email, and had tried a couple of the RP newsgroups on Usenet. In 1995, I tried out Meridian 59 while it was still in beta, but it didn't really appeal to me.
When WebRPG came out, some of my old gaming buddies from high school and I started playing online through it. Later on, we moved to OpenRPG, and still later, to kLooge.WerKs. Around 2000, I started playing in web forum games and did some gaming via IRC. In 2005, I tried my first modern MMO, World of Warcraft, where I've spent a good bit of time hanging out on RP servers, and have written a few RP-focused addons.