I'm looking at the subject of underagers on slash lists mostly from a listmom point of view, because I was two years over the legal age for reading smut here in Belgium. I couldn't/didn't join any lists before I was actually (well, nearly) eighteen, because I didn't want to lie. I just always thought of that as one of these pesky thing about being Belgian when the majority of the rest of fandom lives in the USA, where age laws are ridiculously strict.
So when I started RareSlash, at the whopping age of eighteen and three months, the age thing was really the only rule I consciously thought about and consciously instated. No age statements. Ever, at all. People could be on the list and "admit" to being underage without repercussions from me.
And I've done that on all my lists, always. I've had people warn me, meaning to protect me, I'm sure, that opening up a list like SlashArt to underagers was asking for trouble. (Consequently, when I turned it over to new management, it became an age-closed list. That hurt.) I know I probably am asking for trouble, but it's been nearly three years now, and we're still doing fine on both RareSlash and RS-X, both of whom have no age restriction, and have (had) underaged listmods and, in the case of Rareslash, an underage archivist.
I know I'm risking something, but I'm risking possibly even more with RS-X, and femgeeks, and the whole RPS thing. I'm taking that risk, small as I think it is, because this is something I believe in. I believe that age is irrelevant. I believe that there are twelve-year-olds who are mature enough to discuss subjects such as fisting, water sports, and BDSM, and that there's thirty-year-olds whose reaction to those subjects is "Ew! Gross! You're a pervert and need to be shut up for mentioning that!"
Age is nothing but a number, as us Timbertrickers say. ;D
Which brings us to the other age thing, the subject of underage characters in slash. Now, to be honest, I'm a bit ambivalent about this. Stories where both characters are underage (or at least alike in age) don't bother me. Kids have sex in real life, so there's no reason why they shouldn't have it in fiction, and also, not all slash is smut. Stories where there's a large age difference tend to bother the social worker in me, but I have that with all stories about power imbalances.
More importantly, the fact remains that it's fiction, no matter how bothered you are or aren't by it. No actual children were harmed in the writing of this story. And writing chanslash does not make the writer a pedophile who will go out and abuse a child, any more than the writer of a rapefic is likely to go out and molest someone.
And that's my soapbox for the day.