I think that videogames with their content aren't handled properly when it comes to children. I think that every parent should be able to know what kind of content their children will be able to handle but some parents just don't seem to care about what their kids are doing at all. Violent videogames don't always culture a normal child into being a violent adult but they have been influences in some situations that could have probably been prevented if the children's content was restricted to things that they were mature enough for. I wrote a very very long paper on this last year for my sociology class and there were plenty of studies I found that proved that it was poor content management that made people more aggressive.
The human mind can grow used to any repetitive condition given enough time to accept the condition as normal. You can see this throughout history where what we consider low-grade gore from 40 years ago to be nothing that moves us whereas society 40 years ago was in shock by what little Hollywood has to offer. Today people aren't scared of the old films that our parents and grandparents had nightmares over. We aren't impressed or shaken unless what we see is real enough to be believable.
Now, if you were to let your kid start playing videogames at a young age and they only played games like "gears of war" , a game where you can chainsaw enemies in half, or "call of Duty" , a game that centers around killing others for entertainment (but that's the majority of games these days anyway), they will over time become numb to the violence that they are allowed to experience. They become okay with the actions that they perform in videogames and it does carry over to how they handle things in real life. It doesn't necessarily mean that a kid is going to get up off the couch and go randomly shoot up his neighbors but if the child was in the heat of the moment, he or she would be more likely assault another person who they were angry at. The exact outcomes do vary. Some kids use their fists, others bring daddy's gun to school. It doesn't necessarily have to be videogames that does this either. Playing competitive sports, watching violent TV, hunting and fishing, etc. From the studies I've read violence does breed violence.
Now you know for a fact that you can handle playing GTA. It's fun to rob liquor stores and cause large murderous explosions, but your mature enough to realize the difference between what's real and not real. Young kids have a slight problem with this because they don't always fully understand the difference. The content on videogames should definitely be restricted accordingly by law to varying age groups because leaving your kids to freely explore what's available isn't healthy for their brains. Parents that are caught letting their kids play games that they shouldn't should be punished appropriately but I've yet to come up with a proper punishment suitable for such a semi-petty come that can potentially harm their children or even others. For now I just suggest that parents pay attention to what their children are doing and be sure as possible that they can handle the content they are given.