30 years

I picked up my first roleplaying game book in 1991, when I was eight years old. It was Teenage Mutant Ninja Turtles and Other Strangeness, which as an eight year-old, I thought was some sort of complicated Ninja Turtle comic / choose your own adventure (CYOA) novel crossover. My family was on what I think was March break in South Carolina, and I convinced my father to buy it for me (the main indulgence my parents gave me as a child was books). I was very surprised, upon reading it in detail, that it was in fact a game book, not a comic or CYOA novel. 

In August 1991, I went to a flea market at the school across the street from my childhood home, and found my first set of polyhedral dice (now long lost), a clear orange set someone was selling off with the rest of their AD&D stuff. I bought them for $5, the entirety of my allowance at the time. Shortly after acquiring dice, I began running my first "campaign" with my friends, a mostly incoherent collection of combat scenes involving various characters we had all created battling the Foot ninja clan. I like to think I've improved slightly in the intervening decades.

Overall, it's been a good thirty years of gaming. Here's hoping for at least another thirty.