"Too Short a Season" shows Admiral Jameson as a doddering old man in his 70s.
...And cursing his ailment for preventing him from pursuing an active career as a starship captain
at that age! If anything, I'd take the episode as further proof that people live longer in that time and age. That is, although they still spend their last three decades addled in various ways, they now remain active till their eighties or nineties.
Also, the episode seems to point to this being a "recent" development, because Robert April at a comparable age in "Counter-Clock Incident" was officially declared a useless relic who could no longer serve in a frontline role.