In 2016, Donald Trump became the oldest candidate to be sworn in as president when he was age 70.

Four years later, questions about the age and health of both Mr Biden and Mr Trump loomed throughout an election race that was decided by a younger and more diverse electorate.

Previously, Mr Biden has described himself as a transitional president but hasn't ruled out running for a second term, which had placed a greater focus on his vice-president pick, Kamala Harris, who is more than 20 years his junior.

Mr Biden, in a September interview with CNN, promised to be "totally transparent" about all facets of his health if elected but he hasn't so far specified the details.

His physician, Kevin O'Connor, in a medical report released by the campaign in December, described Mr Biden as "healthy, vigorous … fit to successfully execute the duties of the Presidency, to include those as Chief Executive, Head of State and Commander-in-Chief.".

Mr Trump, after being diagnosed with COVID-19, quickly returned to a busy campaign schedule, some of which flouted coronavirus guidelines including social distancing, wearing masks and avoiding large gatherings.