My humble theory !
Older guys have more life experience and less likely to tolerate being treated poorly by an employer. More likely to point out things which are not fair / reasonable etc etc - some may also say find it harder to pass a TR.
Younger guys tolerate being treated poorly and working for a company that treats you as another way to save money / aka make more profit. May put up more with financial hardships etc etc etc.
I have much more aviation and real world/management experience than a 21 year old so I suspect unsuitable for command was not the reason for not getting the job!
(Would have taken the job had I got it but only because it was a job!!)