Violent Video Games

I was talking to my husband about our media class and the things we've discussed so far.  I brought up the subject of video games, and how there have been studies showing that violent video games and media can have a negative effect on development.  My husband immediately disagreed with me and said that he thinks violent video games have no effect whatsoever (at least for him).  He is really interested in anything to do with history so he really likes the video games that recreate wars and battles of the past, and there's lots of violence that comes with it.  I am not totally against video games, but growing up in my house my brothers were not allowed to play "rated M" games.  So naturally, I don't feel very comfortable with my husband playing these violent games.  He seems convinced that he is not affected, but then it made me think a little deeper.  Do violent video games and other forms of violent media affect us as much when we are older, after our brains have fully developed?  I've heard mixed answers from people about this, but I still think that violence affects us no matter our age.