https://en.wikipedia.org/wiki/National_Minimum_Drinking_Age_...
Plus, it doesn't seem like America is politically interested in lowering the drinking age.
It has already been established that the federal government can't compel states to enact laws or enforce federal ones. [1] (The "federal" drinking age is OK because, IIRC, it was not actually done through direct compulsion, but by conditioning the grant of federal highway funds.) The interesting thing in this case is that the Court has also concluded that the federal government can't forbid a state from enacting a law. Of course, the federal government can still enact its own laws (subject to the Constitution's usual limits on federal power), which would preempt state law. This was a weird case where the federal government tried to do the former but not the latter.
[1] For example, https://en.wikipedia.org/wiki/Printz_v._United_States
[0] https://en.wikipedia.org/wiki/South_Dakota_v._Dole
[1] https://en.wikipedia.org/wiki/National_Federation_of_Indepen...
(IANAL).
IIRC, that's done by allowing states to set their own drinking age, but withholding federal funds for highways unless the drinking age is at least 21. So any state could set a lower drinking age, legally, but they'd be on the hook for making up the difference in funds from their own budget.
That said, the combination of this decision and the ACA ruling that the federal government couldn't withhold funds from non-participating states may provide ground for a challenge to that law.
Lots of adults were alive when that age limit was eighteen. A small handful were alive when it was prohibited entirely. US (still, despite recent politics) receives immigrants from around the world who have a very different culture with regard to alcohol consumption.
An easy way to deter fake ids that was pretty common even a decade ago was to have off duty cops checking ids, so that being discovered can result in jail time instead of just getting kicked out.
They even have apps now that can detect most fake ids.
If you'd like to go on a crusade about prohibition or even access to drugs/controlled substances in general I might be obliged to saddle up with you, but this isn't the straw that is breaking the camels back IMHO