@BrideOfLinux It's NOT a legitimate concern, though. Can he do the job of POTUS? Yes, because he's ALREADY DOING IT. And a damned good job, at that.
If, at some point in the next four years, age does manage to catch up with him, he has a perfectly capable VP to take over. This is a total non-issue, being blown up into ridiculousness by trolls who have nothing else left to try to prop up their pet felon.