Technically the US has no federal drinking age, it’s just that every state has the same drinking age of 21. The federal gov will take away a big chunk of highway funding if they have it lower than 21 if I remember right.

This also leads to the exact specifics of the law being different in each state. Some states only the government can operate liquor stores, some you can buy liquor in grocery stores, sometimes bars let minors in, sometimes 18+, sometimes 21+.