First of all, there is no state law prohibiting alcohol consumption by someone under age of 21 in a private place. State law prohibits possession of alcohol by an underaged person in public place. State law also prohibits selling alcohol to an underaged person.
That being said, his school district may have a different policy. His lease may prohibit alcohol consumption in the premise. These are potential consequences but he did not commit a crime.
Tell him just wait another 5 months if he wants to drink again. And, do not drive under influence.
