In the U.S. we had Prohibition. At the end of that failed experiment, the states were given control over alcohol. That led to some really diverse laws. About the only thing that's consistent is that you must be 21 to purchase alcohol, and you can't drink and drive. Even those rules weren't always the same in all states.
There are state-by-state exceptions to consumption with the 21 age for purchase, usually it's for religious reasons, medical reasons, or if you are in a class where part of the curriculum is tasting alcohol, such as an oenology or brewing class. In Alaska parents can give their kids a drink.

