I wasn't doubting that someone might ask to see ID, and of course they are within their rights to do so. However, in at least some of these examples, it seems that alcohol had been ordered. I would fully expect that to prompt an ID check, if the person ordering looks like they might be underage - and that applies whether or not they had been accompanied into the lounge by a responsible adult.
As for the F Lounge staff checking your age on the computer on the way in - did they actually tell you that's what they were doing? It's pretty standard on entry to international lounges that they scan your BP and/or type info into the computer as you go in. That happens all the time with me - I must admit that I don't know exactly what they are doing, but I'm pretty sure they are not trying to verify that I'm over 18!
Anyway, my point was simply that if they don't ask for ID all the time, then it's worth a try. And they clearly don't ask everyone for ID on the way in, so presumably it relies on the lounge staff suspecting that someone is underage, and bothering to act on that suspicion. IMHO, there is nothing to lose by trying.