Sure, I'll ask where the user is located, and if they choose California, I'll ask them for their age. And if they choose over 21 I'll scold them for voting for Gavin.

Ask where the user is located and if they choose California tell them that your website/service/OS isn't available for users in CA because you will not be complying with this law and they'll have to go elsewhere.

Colorado is trying to copy this law right now, too.