I started on the guitar when I was 18, which means I've been playing the one I have for 4 years now. I've been making music in general since I was 10.
ratbastid is right about technique, self-taught you'll run into problems which will only give you grief down the road. That said :
It all depends on what style you want to play. Classical guitar isn't really something you can teach yourself, but rock guitar is simple enough to learn. I actually started by taking lessons in classical guitar and moved from there to rock by looking up tabulature online for songs I liked. Try
www.guitartabs.cc (assuming you can read tab) if there's any particular song you want to learn.
Aside from an aversion to picks that I keep to this day, I now do better with rock guitar than classical. I've been thinking of taking lessons to correct that, though.