I checked 16-20 (when 21-25 might be more accurate), but only because I was using Legos and Star Wars Micro Machines when I was a kid for RPGing but we didn't know the term yet. Both of my older brothers would run long games where we'd keep track of what had happened in the story (a campaign), I had one character that I played (my PC) who was accompanied by several other friends (NPC party), and we rolled dice (or I'd pick a number between 1 and 5, or I'd draw a card, etc.) in order to determine outcomes of what I tried to do.
Though these games got more formalized and advanced as time went on (eventually ending with a game that didn't use any props, but did include character sheets with stats), I didn't play an official, released RPG until I was 17, which was 10 years ago. So, depending on your view, that's when I started. But I consider my first RPG experience at a much earlier age (at least age 7, but I think even younger). Good times...