One issue that keeps coming up in the presidential race is age: By the time November's election comes around, President Trump will be 74, former vice president Joe Biden will be weeks away from turning 78, and Sen. Bernie Sanders, I-Vt., will be 79.

Either of the Democrats, if victorious, would be the oldest to ever take the office of the presidency. Here is a list of the current five oldest presidents, based on their ages when they took office.

5. Zachary Taylor

Zachary Taylor, the twelfth president, was 64 when his term began on March 4, 1849. His administration did not last long, as Taylor died of cholera in July 1850.

4. James Buchanan

James Buchanan, the fifteenth president, was 65 when he was sworn in on March 4, 1857. He was only president to ever remain a bachelor while in office.

3. William Henry Harrison

William Henry Harrison was 68 when he became the ninth president on March 4, 1841, opting not to wear gloves or a coat when riding on horseback to be sworn in. At the time, he was the oldest to become president and his presidency remains the shortest to this day, as he died on his 32nd day in office as a result of pneumonia.

2. Ronald Reagan

Ronald Reagan, the fortieth president, set a record by being 69 when he took office on Jan. 20, 1981. Reagan remains the oldest person to serve as president, as he was 77 at the end of his second term.

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1. Donald Trump

Donald Trump is the oldest to ever become president, taking office at the age of 70 on Jan. 20, 2017. Should he serve two full terms, he would break Reagan's record as the oldest-ever sitting president.