I have a brother 10 years my junior, so I guess my opinion might be validated.
Tried weaning him on Playstation when he was 5, he preferred jumping around with Mario on N64. As far as violence is concerned, he doesn't really care. One day he'll be playing Diablo 2, the next he'll be playing Mario Kart, the next it might be Gran Turismo. He clocked through Halo over a few days and said it was kinda boring after awhile, which I guess might be reasonable since his main argument was the levels were too bland since he loved walking around in Metroid Prime - this coming from a kid going on 11yrs in a few months.
Other kids might be different, and sure the luster of violence does get him giggling now and again (who doesn't have fun blowing tyres and heads in GTA?) but ultimately he prefers gameplay whether it has violence in it or not it's no concern.
I'm going to bring up my kids the same way, except maybe shove them on Nintendo products first to see how they go, if Nintendo are still alive by then :lol