The studies linking violence in videogames are usually shitilly done. They look at a school shooting or a kid with anger issues, and then they look at the games he plays, and their conclusion is that the videogames are linked to the kids being violent.
The truth is, if you're violent, you'll go out and buy the game that lets you shoot pedestrians, if you like cars, you'll buy the racing game.
I've played violent games since I was old enough to use the keyboard on the computer to play Doom when I was 5 years old. No adverse effects here.
Edit: There was a segment on the news the other day linking action video games to better eyesight.