I have found this to be quite common in the non airline lounges with a bar (e.g. Amex CL, or maybe even ACs), where irrespective of age or how old someone may look they are required to show ID, and also ID for the person you are buying for, and to point at them and they wave, or even worse they have to stand with you.

Other than uniform compliance with laws, it does create a massive queue at the bar due to people having to go one at time, or in pairs etc. And it never ceases to amaze me, how ill prepared people are for their turn - like everyone else has to show ID, and then they are asked and then there is a whole conversation about it, followed by it appears like they have never been in a bar before (and go through all of the drinks before setting on a chardonay!). Not sure why people shut down their brains in the 5 mins they spend idly waiting. But that is humans for you....(see the same in suermarket queues).

Back to the topic, on board never had an issue with offering one glass to a child who is close to 18. Did have the FA on QR take a double take and question when my 13 at the time son, was chugging on a glass of the "So Jenny" (0% rose). Only to check that it was So Jenny.
(We dont in US lounges or US in general as the application of rules are so bizarre - and the tut tutiing from others who despite having pushed one too many into the wind, have decided that they are moral bastion of all).

KF