I started beating off when I was 8 or so, and didn't actually nut until 11. I have had two wet dreams though, one around 14 and the other one in my early 20's. I think that beating off regularly will prevent them usually, but it seems like most guys who have posted so far report at least one or two. I guess beating off regularly will prevent them, with the exception of a few that might get through.
Whatever the case, they're a beautiful thing...