Recommend anime/manga forums for older fans?

Dude! I haven't seen anything remotely close to what you want. You may want to start you own forum for a more adult population. I think it's a cool idea! In any case, check the Baka Updates Manga forums (this is manga only) to see if at least you feel comfortable (since the moderators are always around) but there are a lot of teenagers there so you've been warned!