Pedantically, the law indirectly sets the age for purchasing (and not consuming or possessing) alcohol to 21 by punishing states for not having laws against that, and doesn't directly set the age to 21, but it's effectively the same thing.

Pedantically everywhere except Wisconsin ;) They manage to stay in the good graces of the FedGov while also allowing a parent to take their kid to a bar and buy them a drink.

https://www.revenue.wi.gov/Pages/FAQS/ise-atundrg.aspx