The job of President is grueling if done properly (of course, it’s pretty easy if you just sit around tweeting and not reading or thinking). The extraordinary demands of the position include the ability to nimbly travel across time zones, to function effectively on 4 hours sleep when necessary, and to quickly read, digest, and synthesize many pages of dense writing on complex subjects. I’m in my 60s and am pretty healthy and pretty smart, but there’s no way I’m perky enough to do a good job of Leading the Free World.
From the Washington Post: “Research says septuagenarians struggle with new tasks. That’s bad news for several 2020 candidates.”
Just my opinion here, but I think the president should be younger than 60. Your mileage may vary.