But fiction with sex scenes with minors is not illegal. In the US, in Belgium, or in Finland (I'm a Finn living in Belgium and I believe Insanejournal is US-based?), so there's no chance of you guys getting into trouble. The stuff gets published in dead-tree format, for goodness' sake. I'm not saying you shouldn't use your discretion in weeding out clearly pro-child abuse pornographic material, but I'm not too happy about the idea of not being able to write and post, say, Ginny/Lee fumbling virgin sex in Half-Blood Prince, if I felt like it. There's a slight difference between portraying sex between two teens (something that happens all the time) and imagining twelve-year-olds abused by adults. And on that note, what about fiction that deals realistically with the delicate subject of child abuse, from a non-pornographic point of view and in a manner that could never be called encouraging? How about mention of teen sex without graphic description?
Of course, it's your comm and your rules at your discretion, but I thought I'd let you know how I feel about it.
How about hobbits? They're considered underage until they're 33 (though some marry before that). (This would potentially make my recent Rosie/Marigold smut fic out of bounds, and also every pre- or during-Quest Merry/Pippin.)