My thoughts on this are pretty mixed since I've been reading "adult" material for many years, since well before I was technically of age to do so, and I don't and never did feel particularly disturbed.

Hell, far from being disturbed, I think being exposed to fandom from the age of twelve probably saved me from all sorts of self-hatred by providing me with somewhere where sex and gay people weren't seen as, you know. Evil. Which is probably not an argument that'll get us anywhere with the "protect the children!" folk, but it does make me feel rather strongly about letting the underagers have access, even if it's just the "don't ask, don't tell" method that underage fans have been using for years.