to be President. He was 69.

In general, it is more risky to have a 70+ person as presidential candidate, or as president.

Changes do occur in the early seventies, more in the late seventies, for many people.
Problem is, we often - even usually- don't know which people will experience those changes.

I've observed that Bernie Sanders has exhibited quite a bit of stamina thus far in his daily, rigorous campaigning.
Joe Biden has as well, in what we see of his day-to-day life, including the recent death of his son, Beau.

Disclaimer - I am older than either of these men, and have observed a slowing of energy and other changes in myself.

People worry about the President's health, but if they'd known how ill FDR was, he would have never gotten elected FOUR times! Just imagine how different the last 70+ years would have been without Roosevelt in office.

I think it is important to look at who would be the best person overall for the job. I personally thought McCain was too old when he ran against Obama, not so much in actual years, but mentally he seemed rather erratic and confused. That could be the case with someone younger as well (GW comes to mind).

http://rare.us/story/joe-biden-is-proud-of-creating-harsh-anti-drug-laws-that-his-coke-using-son-wont-have-to-worry-about/

Joe Biden voted for, advocated for, sponsored and even introduced legislation that helped to create and grow the prison-industrial complex that has ruined the lives of hundreds of thousands of lives. This legislation has disproportionately affected poor and minority communities and created a militarization of the police.