
Very early on, my sister decided that the introduction to video games for her now 6 year old would be put off until he was about 7 years old. That's not to say she was trying to limit his exposure completely to video games but to things such as FPS games, Resident Evil type zombies and the like, she felt it best to wait until he was older (older than seven, probably).
My brother on the other hand, is the complete opposite. His son is all about his Super Heroes, blasters, headhunting zombies, fighting games and combat. He is also 6 and his introduction to those types of games happened about a year or so ago.