You do that while I hunt up the number of people who die, have strokes, heart attacks and other debilitating health problems in their 80's or even 70's. Don't care about the 90's as Biden would be 86 at the end of his second term.
John McCain (81, brain cancrer)
Bernie Sanders (78, heart attack)
Ronald Reagan (diagnosed at 83 with Alzheimer's, but showing
symptoms well before.)
We can list people who did well into their 80's, but the chances of being able to cope with the unique challenges, mentally AND physically, that come with being the POTUS drastically decline with age.
Feeding the dog has top priority!