Says who?
I was 7 when I started gaming. I was 8 when I was playing Wasteland 1.
My daughter is 4 and she plays some games.
Four isn't too young for online gaming. Stick the kid in a clan and let some random advlts raise them.
He will fluent in the universal abbreviation lingo that is spoken on the internet.
My 6 year old plays a few pc games. Well most are educational. Jumpstart and a few other sites that teach reading. She does also play Star Wars the Old Republic. Sort of. She likes to raise a smuggler up to 10 or so to get Corso (because her Mother likes Corso). Then makes another and does it all over again. She gets into the Sims as well. Plus another Sims game for the Wii.
Other than that, she is outdoors, at her dance class or playing with her toys.