In his second term as president, Dwight Eisenhower looked like an old man. He’d had a serious heart attack in 1955, requiring extensive hospitalization. He later suffered a stroke. He famously played a lot of golf. In contrast to Ike’s seeming senescence, his successor, John F. Kennedy, seemed vibrant and flamboyant.

The reality was that Eisenhower wasn’t really that old – he was just 62 when he was first elected. And Kennedy wasn’t that vigorous, and indeed was secretly afflicted by serious medical problems, including Addison’s disease, that his aides concealed from the public.

The history of the presidency includes a running thread of illness and incapacity, much of it hidden from the public out of political calculation. A stroke incapacitated Woodrow Wilson in 1919, for example, but the public had no inkling until many months later. And when Grover Cleveland needed surgery in 1893 to remove a cancerous tumor in his mouth, he did it secretly, on a friend’s yacht cruising through Long Island Sound.

Presidential history reveals a more subtle trend: Age isn’t what it used to be. American culture has redefined old age, pushing it back significantly as people live longer and expect to be more active into their eighth or ninth decade or beyond.

Hillary Clinton is 68, and Donald Trump is 70. They’re the oldest pair of major party candidates in history. If elected, Clinton would be the second-oldest person to assume the presidency, after Ronald Reagan. Trump would be the oldest. The relative agedness – call it maturity – of the two candidates this year hasn’t gotten a great deal of attention until recent days.

But health has suddenly become a preoccupation on the campaign trail in the wake of Clinton’s wobbly episode Sunday at the 9/11 memorial service in New York City. The Clinton camp initially called it merely a case of overheating. Late in the day the campaign revealed that, in fact, she was diagnosed with pneumonia on Friday. On Monday, a Clinton spokesperson acknowledged that the campaign could have been more forthcoming on Sunday.

Neither candidate has released detailed medical records. Trump has released only a brief letter from a family doctor declaring, without evidence, that if elected Trump would be “the healthiest individual ever elected to the presidency.”

Clinton’s gender gives her an advantage on one respect: Women in the United States outlive men by several years. According to the Social Security Administration’s online life expectancy calculator, a woman of Clinton’s age is likely to live an additional 18.4 years. A man of Trump’s age is likely to live an additional 15.2.

Voters will have to determine if the murky health status of Clinton and Trump should be a factor in the November decision. What’s certain is that the campaign trail can be brutal, and the presidency itself can pound away at the health of whoever occupies the Oval Office.

President Cleveland kept his cancer surgery secret in part because cancer at the time was such a dreaded disease. He also didn’t trust reporters, and didn’t think his medical condition was anyone’s business, Cleveland biographer Matthew Algeo, author of “The President is a Sick Man,” told The Washington Post.

Algeo makes a broader observation: The desire for secrecy led many American presidents to avoid the best doctors.

“With presidents, a lot of times they don’t get the best care. You would expect they would, but they’re so paranoid about anyone knowing what’s wrong with them that they employ old family doctors,” Algeo said.

The public had limited information about Franklin Delano Roosevelt’s physical condition and the fact that he used a wheelchair. By the time he ran for a fourth term in 1944, he had heart disease, was constantly tired and had trouble concentrating. Frank Lahey, a surgeon who examined Roosevelt, wrote a memo saying FDR would never survive another four-year term. The memo was not disclosed until 2011.

Harry Truman, FDR’s new running mate, was shocked when he saw Roosevelt for the first time in a year, because, as he told an aide, “physically he’s just going to pieces” – a moment recounted in Michael Beschloss’s book “The Conquerors.” When a friend told Truman to take a close look at the White House because he would soon be living there, Truman answered, “I’m afraid I am, and it scares the hell out of me.”

But the public didn’t know any of this, Beschloss writes. Roosevelt’s opponent, Thomas Dewey, derided “tired old men” in the White House, but Roosevelt sailed to victory that November. He died just months later, in April 1945, leaving Truman to close out World War II. Truman had known nothing of the Manhattan Project, and had to make the difficult decision about dropping atomic bombs on Japan.

Kennedy suffered from Addison’s disease and had to take steroids and other drugs to ward off the symptoms, but he did so secretly. As the Los Angeles Times reported: “During the 1960 campaign, Kennedy’s opponents said he had Addison’s. His physicians released a cleverly worded statement saying that he did not have Addison’s disease caused by tuberculosis, and the matter was dropped. Kennedy collapsed twice because of the disease: once at the end of a parade during an election campaign and once on a congressional visit to Britain.”

Historian Robert Dallek told The Post that public disclosure of Kennedy’s health problems could have kept him from becoming president. But Dallek offers a different perspective about the health challenges facing political leaders. He said lethal cancer should prevent someone from running for president, but other health problems aren’t disqualifying.

“Franklin Roosevelt was a paraplegic and he served there for 12 years. Now, Kennedy had all these health issues, and he did a fine job as president,” Dallek said. “You overcome challenges, disabilities. And that was true with Franklin Roosevelt and it served FDR brilliantly in the presidency because people in the Depression thought he had recovered from his polio and now he’s the one to lead the country through a recovery, so psychologically it gave him a hold on the public that was really helpful.”

Reagan’s age was an issue during his bid for the presidency in 1980. But he appeared vigorous when he first took office, regularly lifted weights, and rode horses on his ranch. He survived a nearly fatal gunshot wound early in his first term. Running for reelection in 1984, he appeared confused during the first debate with his opponent, Walter Mondale, but recovered nicely in the next debate by joking that he would not exploit for political purposes his opponent’s “youth and inexperience.”

Reagan was diagnosed with Alzheimer’s disease in 1994. Journalists and historians – and even Reagan’s son Ronald Jr. — have speculated that he showed signs of the disease in his second term, when he was in his mid-70s. That remains a contentious topic, and many aides have insisted that Reagan did not have the disease while in office.