I'll stay a bit off topic - - you said, "they changed it back to 21" -
until 1984 when the federal goverment held highway funds hostage, states were responsible for setting their own age - and many had it lower than 21 - there was just no way to study or come to a valid conclusion until after a change.
afterward, it seemed to have an affect on highway fatalities, but they also lowered the speed limit, made cars safer, made seatbelts mandantory, and instituted alcohol education programs during that time
and now the proponents of a "State's right" to lower it again are armed with 20 yrs of data showing it had the opposite effect intended
peace
ps: my brother-in-law is a Brewmaster, overseeing operations at 3 micro-breweries, so my view is somewhat tempered by the fact that - - -
"he goes to work everyday and drinks beer as his job" (my over-simplified description)