(NewsNation) — President Joe Biden said in a new interview that concerns about his age are “totally legitimate” as questions swirl around whether he will run for reelection in 2024.

During the interview with ABC’s David Muir, Biden, 80, was asked whether he is considering his age when deciding whether to run again, to which he replied no. However, he said it is “legitimate” for people to raise concerns about it.

Dr. Anthony Harris, CEO of HFitHealth, said when looking at a decline as people age, there are two factors: physical decline and cognitive decline. He said evidence has shown people start to decline in their 60s, but that decline accelerates in their 70s, and 80s.

“When we talk about cognitive, these are perhaps, for the presidency, the most concerning, which is our cognitive ability to what’s called crystalline ability, and that’s to recall long-term things, memory vocabulary,” Harris explained. “Certainly, those cognitive fluid abilities are concerning as well, when we’re talking about processing new information, how quickly we do that those things decline as we age, and that’s a natural process.”

Biden, the oldest president in U.S. history, would be 82 when sworn in if reelected in 2024.

The Hill contributed to this report.