There are reasons for a game having a restricted age on them. I play a lot of combat games like Call of Duty and GTA which are directed towards adults like myself. I found that the Nintendo Wii is more directed towards kids.
Well the thoughts of kids out there playing GTA and games like that is pretty unnerving, but I am sad to report that it is often the case. I used to work with kids, and it was amazing how many of them played these games, and these kids were about six to nine years old. I just do not think they are ready for the violence in these games, and I hope that parents are out there watching what their kids play.
You can only hide the vulgarities from the world for a certain amount of time before your child wants to explore them. Mario Kart isn't very harmful for a game, and I think that it's great that your daughter has the chance to play it online with friends! I remember that when I was younger, my first Mario Kart was on the GameBoy and the only thing kids could use to play together was a connector thing. Unfortunately, I didn't have other friends that were into games, so I had to fly solo. I think that games like Mario Kart are really harmless online, but it might be more mature games where you have to draw boundaries, at LEAST until she's a teen. These are the types of games where people might be vulgar online. There's only so much you can do while playing video games online, however. If she's already been exposed to curse words, I don't see much trouble in letting her play online. You just would need to reinforce that she doesn't meet strangers online and try to befriend them or meet up with them in person, though.
I can't just say categorically what age will be okay for kids to start playing online. I'd say it depends on their rate of development too. That said I am thinking from fifteen years will be fine.
