If needing to evacuate an aircraft down the slides is something that there was even a 0.1% chance of ever happening to me then this might be a factor I would consider when choosing an airline.
But it isn't.
As an analogy, do you choose the restaurant where you eat dinner by the quality of the fire-fighting equipment? I suspect you don't, because the chances of you being in a fire in that restaurant are infinitesimal.
I trust the licensing authorities (be it for airlines or restaurants) to maintain a level of safety which means that the chances of being involved in an accident are so small that they are not a factor in my choice of restaurant or airline. (Except that I would avoid those airlines who, statistically have accident rates well above the industry norm: Korean, China Airlines, PIA, Garuda, etc.)
I then choose my restaurant or airline on the quality of the service it provides. This is a function of price, environment, food & drink and the servers who provide it. Fortunately, as I get older (& richer), price becomes less of an issue. In a restaurant the balance is, perhaps, 20% environment, 60% food&drink and 20% servers. On a long haul flight it is more like 40% environment, 30%food&drink, 30% servers. (I do more or less all of my flying these days in business or first, where the food and drink can be an experience to enjoy)
There are many elements to what constitues good service, but undoubtedly as a warm-blooded male, the attractiveness of the female cabin crew is a significant factor (and attractiveness in this context is about appearance and attitude more than intellect since this is a fleeting acquaintance not a long term relationship).
However, I don't think age per se is a good test of attractiveness - I was sat next to a very attractive lady on Concorde earlier this week who I was stunned to discover, as she filled in her immigration papers, was 70 years old - I thought from her appearance and demeanour that she was in her early 50s.
Nonetheless, in general there is some correlation between age and attractiveness, and I can't think of a better objective test. Clearly if, for example, a crew member gets letters of praise from passengers every week then this should override any other consideration.
It is undoubtedly true that a much larger proportion of older cabin crew have attitudes which are unattractive to passengers, particularly on US-based carriers - I don't really understand why, guess it is just a function of boredom with the job. Strangely, on BA I find the male cabin crew to have, on average, a much more attractive attitude than the female cabin crew, regardless of age.
By the way, just out of curiosity, could one of the cabin crew here give me some indication of how common personal commendations from passengers actually are? Is it a major event if you get one, or can a reasonably good crew member expect to get quite a few during their career?
[Apologies for the length of that ramble
]