Er, I don't see how bad customer service has that much to do with age. Look around you at stores, fast food restaurants, etc. where young people make up the majority of the employees. Service sucks. To me the obvious answer is because they are minimum wage employees.
At my regional like most other regionals we have more young FAs than older FAs. In my 2+ years here I've seen crappy young FAs, crappy older FAs, great young FAs and great older FAs. In fact I personally think the young ones tend to be less professional and have a more carefree attitude about their job.
It's true that in some of the Asian countries the FAs are young and the service is awesome... but that has everything to do with the airlines over there. Their hiring process is very selective and even rigorous, and they can afford to be because FA still considered is a decent respectable job in some of those countries. More importantly, the company culture is all about customer service. It's a top-down thing... if the company doesnt emphasize customer service and the employees see that their managers don't give a crap, how do you expect the employees to bother?
I dont see how this dress thing is even an issue... I've seen chubby FAs but nowhere near size 28... I mean you would seriously have to be OBESE like 250-300 pounds to be size 28 and I've never seen an FA nearly that fat.