You are way overprotective, I'm 16 and I've been playing MMO's since 2005, starting from WoW to Lotro, my parents didn't really pay attention to what I played and did It negatively affect me ? No it didn't, it did the opposite. I met new people from different countries and cultures, I also improved my english (Live in Sweden) Hell I could even say that MMO's have helped me mature more than other people in my age.
And also, I've been reading the reasons on why you want to have age requirements, and excuse me but they are kinda silly. One of the reasons that bothered me was the cussing issue, seriously, cussing doesn't affect ''kids'' as you call us, as much as you think it does.