If you sign up for a slot card or anything, they will require ID... and probably refuse to give you since you are underage.

Also - on certain games, if you win a "hand pay" or anything above... something like $1200?? (I'm sure someone will correct me if I'm wrong...), they will will require ID for tax purposes.

Would be a shame to hit a Jackpot for 2 million dollars - and have the casino refuse to pay on the grounds you weren't old enough to be gambling...