The discussion appears to be based on 2 factors...
1. fairness, &
2. competency
on the first matter, nothing in life apparently is necessarily fair; it's a dog eat dog world. If you expect to be given anything by right, then maybe go live in Cuba or Greece, they still have privilege based programs.
On the latter, the funny pages are replete with historical events that have involved disasters caused by wrong thinking and incompetence of the operators. If this was going to determine the fitness of any pilot to operate, then it would result in the grounding of almost all aircraft, as incompetence can be shown for all ages from 18-65. In fact, the only ages where there is no evidence of loss of competency is over 65... (just a matter of time). A pilot that is dangerous at 25 may or may not change his/her "spots"; personal experience has been discouraging on expectation of any substantive change of a personality over time. Situational awareness may improve in part by learning better coping mechanisms, but in general poor decision making, risk taking and manipulative skills do not often improve. Still, the recent history of mind numbing messes indicate a failure of competency of staggering proportions that are unrelated to age, more related to the decay of basic skills, which if anything are inverse to age.
Demanding that a competent operator should give up his/her occupation/career is fairly self serving and rather myopic; given luck all will attain the ripe old age of 45, 50, 53, 55, 58 60, 63, 65 (or unlimited...) that have been the constraining ages just in my experience of the industry. personally, I have watched an older fortunate group ride the age wave over the years and they have had a unique opportunity. Someone else having good fortune is hardly a reason to complain, it smacks of that fascinating characteristic of running a coin down the side of an exotic car, as it is not "yours".
"Calamities are of two kinds: misfortunes to ourselves, and good fortune to others."
Ambrose Bierce, (1842-1914) The Devil's Dictionary
The industry has become a sausage factory; as an individual, if you don't like it, then there are opportunities to use your skill sets in other fields, and looking on the bright side, the constraints to changing employment is diminishing with every case where the system is cheapened. A look around will show that there are a surprising number of occupations that pay far better now than almost all pilot positions, and the conditions of serv(itude) that exist in most companies today are worse than those that exist in alternative service. In fact the question really should be asked, why on earth would anyone want to stay in the business, and the most likely answer is that a lot of people actually get some professional pride in the industry despite the cheapening and demeaning of the profession that has become commonplace.
Stay, go, whatever; just please don't wake me in snooze... unless it is for more coffee or an EGPWS type IV or II alert...