"Today the Supreme Court agreed to hear California's appeal of a unanimous 9th Circuit decision (PDF) that last year struck down a 2005 state law banning the sale or rental of violent video games to minors."The article is short but more lucid and informative in its presentation than the mainstream newspapers or gameblogs have managed to be.

My gut feeling about it is that something like the movie ratings would be sufficient, but it has to be enforceable and maybe that can only be done by (terrible idea alert) having players tied to an ID/credit card and logging in every time they play.
'Cos really, you don't want to have elementary school kids ingesting 24 hours of GTA each week. Books and movies are just "watching," but video games, you're DOING the killing, in a real psychological way. Not that kids are gonna steal motorcycles and throw C4 around the airports or nuthin', but... you're training them to have a worldview that will then need to be unlearned, and in the meantime you have them getting all half-assedly belligerent in the mall.