well considering alot of retirement homes have Wii's to give old people easy excercise activities there probably is no 'acceptable' age limit these days.
i know alot of old adults that play games like golf on their computer. shooters i'd think would be acceptable for anyone up to 40'sh, but i really look at it as a generation thing. I think theres a cutoff around that point where the 'videogame' generation grew up.
i think serious videogaming is still socially unnaceptable at some point, but casually its ok at any age.