One of the side problems is that there are a lot of punks in any multiplayer games who have nothing better to do than spam foul language over the player chat.
For age, I'm not sure. My kids are too young. I let my son watch me play once in awhile (he's 7), and he has a lot of questions about good guys and bad guys, etc. I let him play with it a bit on an empty server, but I feel he's too young to get too involved with it. I played with Clans that had ages range from 14 to 60, and everyone handled themselves very well, even the younger players, but playing on a carefully moderated server helps a lot.