The second hour of the debate began with conversation about age — and how much it matters.

Moderator Tim Alberta, chief political correspondent for Politico, broached the subject with the three oldest candidates: Sen. Bernie Sanders (D-Vt.), who is 78, and then former vice president Joe Biden, who is 77.

Then he turned to Sen. Elizabeth Warren (D-Mass.), who is 70.

“Senator Warren, you would be the oldest president ever inaugurated,” Alberta said. “I’d like you to weigh in on this as well.”

Warren had an answer at the ready.

“I’d also be the youngest woman ever inaugurated,” she said, grinning.

The crowd erupted in cheers. On Twitter, viewers and analysts commended what seemed, to all, to be the ultimate witty comeback.

Rep. Ayanna Pressley (D-Mass.), who has endorsed Warren for President, tweeted Warren’s quote, with an attribution that suggests her words will go down in history.

Age has been a central issue in the 2020 campaign, as three septuagenarians have consistently led the polls. Of the three, Warren has received the least scrutiny for her age — likely both because she is considerably younger than Biden and Sanders, and because she, by many accounts, “looks young.”

She is known for running through crowds of supporters at campaign events and standing in “selfie lines” for hours. At a recent rally in Rock Hill, S.C., a local councilwoman, Nikita Jackson, commended Warren on her “energy” and “stamina.”

“I was just amazed that when you first came out here, Sen. Warren, that you ran up those steps the way that you did, and all this energy and stamina that you have,” she said.

It appears that’s the energy that Warren is bringing to the debate tonight.

Biden took credit for putting RBG, Kagan and Sotomayor on the Supreme Court. But he left out Clarence Thomas.

It struck many viewers as tone-deaf

Caucusing in Iowa can take hours. What are you supposed to do with your kids?

It’s not as simple as hiring a babysitter

Why are young people turning their backs on Elizabeth Warren?

Eighteen- to 29-year-olds in Iowa are flocking to Bernie Sanders