-First, what kinda violence restrictions.
I mean, I played Mortal Kombat when I was like 5, Resident evil at 10, American McGee's Alice at 14.
It depends on the kind of kid, I mean, I know that s**t like pedophilia and rape are bad, I even hate it, but in videogames and anime, well, I like it, I've played RapeLay since I was 15, I like it, but not for that I'm going to go raping little 9 year olds, I mean it's a game.
Not because a kid sees it in a game it's going to do it, and the job of a parent is to acknowledge the kid what the deal is, Like where the baby's come from, it's better to talk about that like when the kid is 5 or 6 years old because that way the kid doesn't get it with perversion, but like something normal. So I don't think that games must have a limit, they just need like a warning of the games content, like the ratings have, so that way, you know exactly what your buying (or downloading , I dont even care), but just telling the children that is a game and not to try imitating the action seen in said games.
P.S: used to play Mortal Kombat 2 all the time with my mom, she always kicked my ass.