OP i think your being a bit too protective here. GTA was released in 1997. I would have been 12. Everyone I knew at school was playing it.
Your opening up your kid to be bullied here IMO if he's the only one out of his mates not playing COD or titanfall, etc. They are normal games for me. COD seriously i'd let a 5 year old play it. it's a game after all.
I'm not saying let him play GTA as he's a bit young however I wouldn't stop say a 13 year old from playing GTA and it has stuff like drugs, sex and prostitutes in it. Hell at 13 kids at my school were all smoking, drinking and having sex. A girl in my class left because she was pregnant around then too and she wasn't the only one.
I play Destiny with a few lads around the 17-18 age and guess what they are up to at the weekends. Taking drugs, etc.
Sticking your kid in a bubble is the worst way to educate them on these things as they are programmed to rebel.
you'd be surprised. the younger he starts the easier it will get with time and he'll pick it up quicker than older people. the better a player he will be in future than if he starts playing games with lots of mechanics later on and sticks to dumb games for now.
there was a video on reddit for instance of a 5 year old playing destiny as a titan with a shotgun and twilight garrison. he was wrecking people int he crucible too with his moves that would embarrass most of us.