Joe Biden, the oldest person ever in the US presidency, said Friday it's his "intention" to run again in 2024 and that his wife Jill thinks he should not "walk away."

Biden's comments in an interview with MSNBC addressed a question fascinating Washington watchers as Biden approaches his 80th birthday next month.

"I have not made that formal decision but it's my intention, my intention to run again, and we have time to make that decision," Biden told MSNBC.

Asked what the first lady, who is widely judged to be a powerful voice behind the scenes in the White House, thinks of him seeking a second term, Biden indicated she was in favor.

"Dr Biden, my wife, thinks that we're doing something very important and that I shouldn't walk away from it," he said.

Biden has previously said he wants to run, but at times has also sown doubts. In an interview in September with CBS, he said it was "much too early" and his decision "remains to be seen."

He also called himself in that interview "a great respecter of fate."

In Friday's comments, Biden went further than before in explaining his reasoning about what would be a mold-breaking candidacy. If re-elected, he would be 86 by the time he finished his second term.

Biden hinted -- as he has before -- that an attempt by Donald Trump to return to the White House might be his motivation to seek the grueling job again.

He said his son Beau, who died in 2015, would have told him to run "depending on who the opponent is."

"If they have a view that is the antithesis of what I believe is democracy and is good for average Americans," Biden said, then Beau would tell him: "Dad, you have an obligation."

Biden also offered an explanation for why he has not explicitly announced a decision, noting that this would change his legal status and "once I make that judgement a whole series of regulations kick in and I have to treat myself as a candidate from that moment on."

Pressure will grow on Biden to clarify his plans after the midterm elections on November 8, where his Democratic party is currently expected to lose control of Congress to the Republicans.

Speculation is rife that Trump, who faces multiple legal challenges and oversaw an unprecedented attempt to refuse concession to Biden's victory in 2020, will try to come back in the 2024 race.