Tell him you'll see him in court. The email sounds like good evidence that the ticket and drinks were a gift. Once a gift is given, the law doesn't allow the person who made the gift to change his mind and demand the gift's return.
I wouldn't say that he was contributing to the delinquency of a minor, unless you were under 18 at the time. However, it is illegal to buy alcohol for a minor, so if he's claiming there was a contract for him to do that for you, it's unenforceable as is any contract to do something illegal.