Although people (mainly adults) seem to think that the younger generation spends too much time playing video games, why set a time limit? As well as being difficult to set in place for the companies that produce these games, it would frustrate many a gamer and set these companies back a few thousand dollars.
Perhaps if a parent sees their child playing video games for long periods of time, they could just suggest something else, rather than have every video game restricted to a certain time. Gaming is something young people do to have fun and pass time. If they'd rather play video games than interact with friends or family, that would be a bigger concern.