If he said WoW, I would've agreed, that game and any MMO should be AO and carry a very big warning label and a quick-dial to the nearest psychiatric clinic. Video games are in dozes larger than 2 hours per day detrimental to one's childhood, but whether they are violent or not is less important, more important is the atmosphere of the game and its general message. I wouldn't even blink if i saw a 7 year old play God of War or GTA, but games like postal will screw anyone up.
Kids need an active and (direct)social lifestyle to grow up healthy, but games that fall within their age are no worse than any other detached passive activities like watching TV, playing with toys, reading or surfing the internet.