Democratic presidential candidate Julián Castro greets people Thursday at the Democratic presidential primary debate in Houston. (David J. Phillip/AP)

Democratic White House hopeful Julián Castro insisted Friday that his questioning of Joe Biden’s memory during the previous night’s debate had nothing to do with the former vice president’s age, although he also referred to Biden in the same television interview as someone who’s “been around for a long time” and had trouble hearing him.

Castro, a former housing and urban development secretary, was pressed during an appearance on CNN about one of the most memorable moments from Thursday night’s debate in Houston: an exchange about health care in which Castro asked Biden, “Are you forgetting what you said two minutes ago?”

Castro’s assertion that Biden, 76, contradicted what he had just said about his health-care plan did not fully square with Biden’s words.

In touting his plan to expand the Affordable Care Act with an optional public insurance program, Biden said, “Anyone who can’t afford it gets automatically enrolled in the Medicare-type option we have.”

Shortly afterward, Castro accused Biden of having said his plan would “require them to opt in” — and pointed to that as a difference between his plan and Biden’s plan.

During the CNN interview, Castro noted another point in the debate in which Biden said those who lose insurance from their employers “automatically can buy in” to the proposed expanded Medicare program.

“He had in fact said those words but then he denied saying them,” Castro said Friday on CNN.

Castro insisted that he was not making insinuations about the former vice president’s age when asked why he repeated the question about his memory two more times during the debate exchange.

“Number one, he couldn’t hear me in the auditorium,” Castro said of Biden. “Secondly, look, that’s a question that I would ask any opponent in a debate.”

Castro said he treated Biden no differently than he would any other candidate.

“The vice president, is, you know, I mean he’s been around for a long time. Okay, when we’re up there, we’re up there to debate,” Castro said. “It didn’t matter that it was Joe Biden. If it had been another candidate who tried to deny what they said just two minutes ago, I would have asked them the same thing.”

He added that he had no regrets about how the exchange played out.

“I’m going to continue to point out the differences,” Castro said. “I’m glad we had the opportunity to have that exchange.”

Sean Sullivan contributed to this report.