The “age question” that burst into the open in last week’s debate got some fresh validation Tuesday from an unlikely source: Former president Jimmy Carter said there should be a limit on the age of a president, and that he didn’t think he could have done it well at 80.

Polling bears out that a sizable number of Democrats have some concerns about nominating a candidate who is over 70, or at least they would prefer someone younger. In the most recent Washington Post-ABC poll, nearly 60 percent of Democrats said age does not matter when it comes to the Democratic nominee’s likelihood of beating President Trump. Four in 10 said the nominee needs to be under 70 years old.

That rubs up against the reality of the race to be their nominee: Most Democratic voters are rallying behind the three oldest candidates in their primary field.

All three candidates in the top tier of the Democratic field are at least 70: Former vice president Joe Biden is 76, Sen. Elizabeth Warren (D.-Mass.) is 70 and Sen. Bernie Sanders (I-Vt.) is 78. The three combined for 66 percent of the support of Democratic voters, according to the most recent Post/ABC poll. A poll from NBC and the Wall Street Journal released Tuesday has their combined support at 70 percent among likely Democratic primary- or caucus-goers.

Claudia Mrozek, a 75-year-old Scottsdale, Ariz., resident, said that the Democratic nominee needs to be someone younger than 70 — or at least someone who is young in thinking.

“A lot of voters want to feel secure with someone who is very familiar with the job or who has done it before — like Biden,” she told the Fix. “Personally, I feel they are ready for someone who is younger and has energy and brings new ideas to the table.”

The 94-year-old Carter, who served as president when he was in his 50s, didn’t say what he thinks the age limit should be. He noted that he does not believe he could have done the job well as an 80-year-old.

“You know, if I were just 80 years old, if I was 15 years younger, I don’t believe I could undertake the duties that I experienced when I was president,” he said Tuesday. “For one thing, you have to be very flexible with your mind. You have to be able to go from one subject to another and concentrate on each one adequately and then put them all together in a comprehensive way.”

Biden or Sanders would turn 80 during their first term in office, if elected. Trump, who is now 73, isn’t that far behind.

Following the outcome of the 2018 midterm elections, the success of these older candidates is in some ways surprising. The races were largely viewed as a referendum on Trump, but they were also viewed as a mandate to the country’s political leaders: It was time to expand the number of new and younger voices at the decision-making table.

And data released as recently as May supports that position. Only 3 percent of Democrats said the best age for president is in their 70s, according to a Pew Research Center poll. That was in the abstract.

Fred Vearnon, a 76-year-old from Pittsburgh, said a younger nominee is necessary to focus on the issues of the future.

“When you’re over 70, you’re thinking ‘old school.’ The world is not old school anymore. You’ve got climate change. You’ve got cities in 10 years that will be under water. You’ve got to think new,” he told the Fix.

What support for these candidates could be showing is that while being in one’s 70s might not be the ideal age for Democratic voters looking to replace Trump, Biden, Warren and Sanders carry some of the traits Democratic voters find most attractive in this moment.

Trump’s presidency has been plagued by low job-approval ratings from its earliest days. The president who campaigned as an outsider interested in cleaning up the swamp has made it murkier, according to his critics. The Washington outsider regularly displays a lack of familiarity with government.

It is this frustration that draws many supporters of Biden to the veteran lawmaker who argues that his experience in Washington makes him the most qualified person to pursue the White House. After all, he was in Washington before some of his competitors in the race (Rep. Tulsi Gabbard of Hawaii and South Bend, Ind., Mayor Pete Buttigieg) were even born.

There have been a few instances recently that put Biden’s mental sharpness into question. Former HUD secretary Julián Castro’s confrontation of Biden on his memory in last week’s debate brought those to the forefront.

But those concerns have not kept 45 percent of Democrats from believing that Biden, according to The Post’s most recent poll, has the best chance of beating Trump in a general election. Biden would be the oldest person sworn into the presidency if elected.

Interest in Biden, Sanders and Warren in particular has remained steady. More than four in 10 voters who lean Democratic have strongly favorable views of these three candidates, showing that enthusiasm accompanies many voters support — an important indicator when it comes to measuring turn out. Whatever anxiety some Democratic voters have about backing older candidates, up to this point, has not ultimately been reflected in the polls when they consider actual candidates.