Originally Posted by
DCAproducer
As far as I have been told before by airline folks, the drinking age on any flight is dependent on the carrier's Flag. DL is a U.S. carrier, hence the drinking age on any of their flights is 21. This includes international.
from what I understand the US drinking age statutes are actually under State jurisdiction and not federal. The federal government essentially blackmails state governments by threatening to withhold highway money if the states don't have a minimum age of 21. I'm not sure which state law the airplanes would have to enforce, since there are differences between them.