Roughly a decade ago I was in transit in the NZ LAX lounge on NZ1, and casually chatting to a young lady who had been upgraded to Business Class, having connected from an AF flight from CDG. She was not legal age to drink in California (possibly not even NZ), and asked me if it was ok for her to have a glass of champagne. I said that it was really up to the lounge staff, so she went off, came back with a glass and enjoyed it.
She had just come back from a year as an exchange student in France after all, so didn't think anything of it. She had learned that one can drink to enjoy it, rather than to become paralytic.
Of course, given she was unaccompanied, I presume the LAX lounge staff figured she would hardly have been an issue. Whether she told her parents when she got back to NZ is another story!