It makes absolutely no sense to single out 20 year old adults from the rest of their fellow twenty somethings. Time to change the drinking age laws from 21 to 20.
When I was 18 in 1967 I could legally drink in many US jurisdictions, and did. US military service members could also drink at 18 in service clubs on Federal military reservations. Even when they were located within otherwise totally "dry" State Counties where no one could otherwise drink.
But neither could I vote until I was 21. In the 1970s the situation was reversed. You could vote at 18 nationally, but not drink anywhere until 21. Same as today.
I think the legislators who passed the higher universal drinking age law looked at the demographics of drinking-related deaths. Too many teenage deaths and hospitalizations due to alcohol. With great pressure on them from parent groups and others.
I remember some of this, being this very age and affected by it at the time. How they settled on 21 I have no idea. But it may have reflected an age tradition with voting and for other legal purposes in the US.