I'm 22, I'm the DM, and I regularly recruit new players into the hobby via my siblings, the neighbour kids, and their friends. My current group is all 17 and 18 year olds. (Apparently all my friends my own age have too many "responsibilities" that come before playing D&D. lol)
There was, now there is not. We're all in our 30's and 40's, but we had the daughter of one player and her boyfriend playing with us for quite some time; they were 18 and 17. They're both at college now (and still gaming up there) for the forseeable future, so our average age bounced back up. We had no problems with them, except for occassionally having to explain a certain reference to them.