Right, but they still take your word for it initially and then only ban if they are able to prove the opposite. You should have to fax proof of age right from the beggining and that would take care of a large bunch of kids that are costing advertisers. That doesn't mean these kids account for all the fraud of course but it certainly accounts for a lot of it.
I agree that that would be a good idea. Too many seem to think that this is some kind of game, rather than a real business.