Drinking age should be 18 or 19, if you can vote, get married, get drafted you should be able to buy a drink and smokes.
I would be in favor of 18 AND graduated from HS. That was part of the push back when they raised it if I remember correctly.
When I was s freshman it was 21 (and also 21 to vote) and while I was in college it went to 18 in 1972 and back up to 19 in 1973 and than back to 21 by 1986. The 1970's were the true heyday of partying at ISU. Even at 21 the ID checking was pretty lax once you weren't a complete HS looking kid. Fake ID's were abundant and draft cards worked as ID.
States only went back to 21 because they were threatened with losing federal highway funds if they did not. A lot of rationale for lowering to 18 was the Vietnam draft, old enough to to be drafted than you should be old enough to vote and drink.