Will there be a way to ensure whoever joins is indeed 18+? Or will those participating just have to hope and pray that everyone involved is just as honest as Jim in Liar, Liar? 

I agree that 18 should be the rule(Even here in NC, where it seems to be 16), but it seems without a set way to do it, it could be a big risk for people to take - even if they wanted, I mean really wanted, some grown up time textually.