Legal smeagle. I would bet that 99% of people (including boomers) think that 20 year olds should be able to drink. The oft cited argument that "we let 18 year olds man nuclear subs that could take out a city" is just too obvious.
(I got drunk first time when I was 14 and have no strong opinion on when it should be legal to buy alcohol.)
I suspect many would also oppose dropping the legal age for MADD inspired reasons (god I hate that organization.... bunch of neo-prohibitionists...) even though they think their kid is responsible enough.
I do agree though, most probably do think that the age could be lower.