Depends what game you want to talk about. I really didn't play any M games besides first person shooters when I was younger. It's possible I just had anger issues with games. My point is still made that I did not own my first M game until I was 15. The other times I had played an M game were over friends or family on occasions. So you can't use me as an example. Now if you want to look at game content for M games let's take a peak at Grand Theft Auto 5. Go ahead and look at this link and tell me how any of what is described is suitable for children. Most M games contain foul language that when exposed to a younger audience may start being imitated.

Violence influences don't actually have to be physical attacks on others. Ever think of psychological? It's possible you get more violent urges in your mind against people. An example, you see a guy picking on a dog and rather than being charged for animal abuse you instead start having thoughts of ways he should die for what he's done. The violence can get to your head. Thoughts of such are unhealthy. We can go on and on about the content in games and the effects it has or the audience it's suitable for. I'm still saying it's not meant for kids.