When I was still under age I’d order alcohol all the time on CO, either with chits or in F. Either they didn’t ask or asked with a subtle “just-say-you’re-21” sort of hint. Either domestic or international.

If someone could actually point to a regulation that says a US-based carrier must enforce a drinking age, I’d like to see it, but as I recall every time this topic has come up the legal consensus has been that there is no drinking age because state law doesn’t apply on planes or something along those lines.

IANAL.