• Former President Jimmy Carter's grandson credited his longevity to exercise.
• Carter died at 100 on Sunday and was the longest-living president in US history.
• But Jason Carter told Time before his grandfather died that he would have attributed his longevity to his marriage.

The grandson of late President Jimmy Carter said that his grandfather's exercise habits may have contributed to his longevity. 

Carter died on Sunday at 100, making him the longest-living commander-in-chief in US history.

He was treated for brain and liver cancer in 2015, and had been in hospice care since February 2023.

Jason Carter, a former Georgia Democratic state senator and the party's 2014 gubernatorial nominee, told Time in 2023 that his grandfather consistently made an effort to find places to jog during his many travels, and later switched to biking as he grew older. 

He said: "If he got to a new city that he had never been to before, whether there was Secret Service or not, he would say, 'Hey, is there a bike?'"

The former president also previously played tennis daily. 

However, Jason Carter said that his grandfather would likely have credited his longevity to his 77-year marriage with his wife, Rosalynn Carter, who died in 2023.

"The best thing I ever did was marry Rosalynn," the former president said during a 2015 interview at the Carter Center in Atlanta. "That's the pinnacle of my life."

Jimmy Carter served as a Georgia state senator from 1963 to 1967 before his stint as governor from 1971 to 1975.

Running for the White House in the aftermath of the Watergate scandal, he won the 1976 presidential election, defeating then-President Gerald Ford, but lost his reelection bid to former California Gov. Ronald Reagan in 1980.

After leaving Washington, the Carters returned to their native Georgia. The former president received widespread recognition across the globe for his early efforts to combat climate change and his decades-long humanitarian work.

Jason Carter told Time that his grandfather's tenure in the Oval Office was very much a "millennial presidency," noting that many of the policy items that younger Americans currently want to see addressed were things that the former president foresaw in the 1970s and 1980s.

"If we had listened to his presidency when they started talking about climate change, when they started talking about changing the way that we consume energy, solar and alternative sources — we would be far, far ahead of where we are now," he said.

Jason Carter told the Journal-Constitution in August that his grandfather was "more alert and interested in politics and the war in Gaza," and was trying to "make it" to November 2024 to vote for Kamala Harris in the US presidential election.