By Byron York

Here are the ages that the top presidential candidates will be on Inauguration Day, 2021: Bernie Sanders, 79; Joe Biden, 78; Donald Trump, 74; and Elizabeth Warren, 71.

If Sanders were elected and served two terms, he would be in office until age 87. If Biden did the same, he would serve until 86. If President Trump were re-elected, he would serve until 78. If Warren served two terms, she would be 79.

There has never been a moment in American history in which so many of the top contenders for the presidency have been so old. There has never even been a time when two candidates over 70 ran against each other in a general election. Before President Trump, there have been only two presidents who turned 70 in office: Ronald Reagan, who took office at 69 and left at 77, and Dwight Eisenhower, who took office at 62 and left three months after turning 70.

Now, if Sanders or Biden were elected, the president would turn 80 early in his first term. A second term would leave them heading toward 90. That is totally uncharted territory in American politics.

Clearly, with Trump and the top three in the Democratic race all over 70, voters have decided that 70 is not a disqualifying age. But is 80?

That is the question for Biden and Sanders. That is not to say that an 80-year-old president will suffer from dementia, although that would certainly be more of a risk than with a 60-year-old president. It is not to say that an 80-year-old president will suffer physical decline that will make performing the world’s most demanding job more difficult, although that, too, would certainly be more of a risk.

It is to say that there is a reasonable likelihood the president’s age will be an issue throughout his or her time in office.

Reagan’s second term, which began when he was 73, was filled with open discussion that he was losing it.

The talk was quite common in 1987, with the release of the Tower Commission report on the Iran-Contra affair. The report portrayed Reagan as aging and disengaged. “The issue of memory loss and age has been raised by observers of President Reagan and his role in the Iran-Contra affair,” The Washington Post wrote in March 1987. A joke, playing on the old Watergate saying, emerged: “What did the president forget and when did he forget it?”

Of course Reagan, who seven years later would announce he had Alzheimer’s, knew about the talk and characteristically handled it with humor.

Back then, Reagan’s gaffes and misstatements often led to discussions of his age. Now, there is growing attention to Biden’s gaffes and misstatements. Even though he has been known as a “gaffe machine,” Biden’s errors are discussed in the context of his age.

But the age issue in 2020 is about more than just gaffes. It is a substantial question for the nation’s voters. Any of the top contenders might well experience age-related problems in office, and voters need to consider that before electing them.

Byron York is chief political correspondent for The Washington Examiner.