What does it means, that everyone should be allowed to do whatever is good for their business regardless? If it was forbidden everywhere to discriminate F/A because of their sex/age, companies wouldn't be tempted to make more business at the expenses of women. And what should the F/A in question do once they are dismissed because of their age, go throw themselves in a dump? Starve their children because male pax would rather be served by a young pretty thing? Which I refute, btw, because 1)not all pax are men 2)believe it or not some pax are so dumb that they'd rather have a skilled F/A than a nice little thing with years of work before her prior to becoming a skilled F/A.
Have a look at the Manchester accident: the two who perished and were't able to make pax escape through their assigned exits were the most junior and inexperienced. One of them was seen standing in front of the open exit, through which no one was escaping. She couldn't escape either and was found dead in front of it. Unfortunately no one survived to tell us why, and what happened, but sure is that the senior F/A at the FWD doors managed to open the exits, one of which was jammed (and it was the one the CPT had specified to be opened, but since he couldn't get to open it immediately he took the chance to open the other one-and he did right!!) and most of the pax escaped through those exits.
Let me tell you something: even if it were true that pax only wanted young and pretty F/A, it doesn't mean it would be the wisest or the right thing to do. In the event of an accident, what you need is someone skilled enough to save your behind. In a crew there should be men and women, young and less young. Experience is gained even watching the senior work.
Anyway, that rule sounds to me rather hypocritical. Were it not, they should fire all the male F/A, who are really "offending on the eye" of those sex-maniacs MAS think are their pax.