Benton Harbor, Mich. (CNN) Former Vice President Joe Biden said a candidate's age is a "legitimate" issue in elections -- including if he were to run for president in 2020.

"I think age is a totally legitimate thing to raise," Biden said during a question and answer session at the Economic Club of Southwestern Michigan's Speaker Series Tuesday. "I think it's totally appropriate for people to look at me and say if I were to run for office again, 'Well God darn you're old.' Well chronologically I am old."

"Every voter is entitled to know exactly what kind of shape you're in. You owe it to them. It's a legitimate question and so I think age is relevant," he added.

Biden's comments came in response to a question about whether term limits or a mandatory retirement age should be implemented for members of Congress or the Supreme Court.

Biden is currently 75 years old, and if he runs for president in 2020, he would be 77 when the caucus and primary contests get underway. The potential Democratic field includes other possible contenders who would be in their seventies come 2020 -- like Sen. Bernie Sanders and Sen. Elizabeth Warren, currently 77 and 69, respectively. They could face off against a crop of younger possible candidates, like Sen. Cory Booker, currently 49, and Sen. Kamala Harris, currently 53.

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