"After 9pm you must be 19 or older to be admitted, unless accompanied by a parent or guardian. Valid ID is required. Thank you for your cooperation."
Can I hear an "amen!"?
Yesterday was the first day of this and the first big group of teens (~12 of them) to be turned away proved our point that this measure is necessary. When politely told our new policy by our host (the sweetest boy in the world) and not-so-politely asked to step out of the restaurant by the off duty cops we've had as security for the last 6 months, the teenagers started shouting about what bullshit this was as they rowdily backed out of the foyer, and then spent a few minutes banging on the windows shouting "Fuck [name of restaurant]!" and flipping off staff, security, and guests alike.
No, please, come back. We're sorry, you're exactly the people we want dining in our establishment. Our bad.