I don't think they care as long as it's not unreasonable (ie. a 8 year old ordering vodka on the rocks)

Liquor licenses are issued by states and the law varies. Only recently (late 90s) did 21 become the minimum age throughout the US.

I don't think airlines need a license to serve in the air and I don't think the laws apply. FAA requirement for alcohol to be served by a crewmember and for no pax to be intoxicated apply, of course.

I've never seen anyone carded or refused due to age.