My 12yo son plays runescape a lot. He has a little clan of friends. I think a lot of them are the other 7th grade boys from his school, though. I'm guessing you may not want to join up with that crew. Take it from me, 12 and 13 yo boys can be pretty obnoxious. LOL.
My dad and brother are WOW players. I asked my brother about runescape and he told me it is mostly teenagers who can't afford to pay for WOW or whose parents won't let them. I was asking more about safety/security of my son while playing the game and he said it should be fine. He does a lot of online gaming, so he would probably know better than me.

DS can't get online from his bedroom, so we can monitor his online activities from the family room.