Letting the usefulness of this measure aside, I think there should be other ways to get your age without using your ID, like using a credit card for example. I don't know if there is any way to get the age of a person using the credit card, to be honest, but at least is an identification method with a expiring date and possibilities to cancel in any moment, not a unique number you can't never change in your whole life (at least in most Western countries I know).