The drinking age isn't dependent on citizenship or residency, so I don't think it should be a problem.
There was a time when I was younger when the drinking age among states weren't uniform; that was something the Republicans brought in during the Reagan Administration in response to MADD (Mothers Against Drunk Driving.) When I was younger different states and D.C. had different age requirements to drink alcohol == Georgia and D.C. were 18, Florida lowered it to 18 in 1971 in response to the 26th Amendment on the voting age, and other states adopted limits at 19 and 20, and other states kept it at 21. If you lived in a state with a higher age limit, you could go to an area where the drinking age was 18 and legally buy and consume alcohol there.
I know there was a task way back in a early season (probably in Germany) where one team had a member who drunk the beer almost as much as he spent getting the beer-filled steins to the right table; so drinking an alcoholic beverage per se isn't automatically prohibited on the Race, as far as I've ever heard, but I am concerned if the amount to be consumed is to be a large quantity, because binge drinking almost comes against a promise Elise made some seasons back about avoiding any more binge eating tasks after the fans really complained about it.