As (not entirely facetious, at all!) counterpoint to the other answers and comments:
Clearly, "getting older" (whatever this means precisely) is construed as a bad thing, with mostly bad side-effects, by the question, and as an under-current in the answers, even if they push back slightly.
As in my earlier comment, it might be interesting to reflect on the reversed assumptions and corresponding question: "How can young people have any hope of doing meaningful research, being adequate scholars, and competing in the academic marketplace, when they are so immature, inexperienced, ignorant, and naive?"
(I would seriously claim that, although the previous is presently a rhetorical question, it reflects enough reality to bring the question above to more-or-less a "dead heat", I think.)
That is, population X may reasonably imagine (if they are optimistic) that the traits they imagine that they have are exactly what makes them superior (in some useful sense) to other tribes/populations/clans, and can have discussions about how those other populations (purportedly lacking these signal distinctions) can bear their own existence, survive at all, etc.
I've heard all too many times the idea that (in math) "well, when you get old-and-tired and can't do research any more, you can always teach". Toooo many assumptions here, especially that people who lack the energy or interest to continue research "can always" teach. E.g., I'd claim that if they were not good teachers before, loss of energy and interest wouldn't help... (Of course, such comments are in a mythological context where "anyone can teach", but "only the special ones can do research"...)
It is true that in current contexts there is an aggressive identification of "research" with "funding" and "entrepreneurial spin-offs" and "technology transfer". I cannot speak for engineering departments and such, but this is clearly not the model of all departments in universities. Some departments are caught in the middle, e.g., mathematics, where there is a seductive possibility of playing short-term, big-money games (as opposed to small-money, quiet, long-term scholarly games).
I do not claim to understand the arc of personal scholarship, nor the gamut of "economies" of grants and such across disciplines, but it is relatively clear in my experience that there are many scenarios where I'd be very much more interested in hearing a scholarly opinion from a decades-long experience than from a glib newcomer. Sure, newcomer rebels can be interesting, but the context is complicated.
So, my facetious-rhetorical response is "What? I'm getting older?" (Sincere!) And, then, "Wait, what, all this time I thought I was finally figuring out how to do stuff, I'm being declared ever-more-incompetent?!?!"