The Oldest US Presidents

	Born	Elected	Age	Took Office	Age	Left Office	Age
Reagan	6 February 1911	4 November 1980	69 years 275 days	20 January 1981	69 years 349 days	20 January 1989	77 years 349 days
Trump	14 June 1946	8 November 2016	70 years 147 days	20 January 2017	70 years 214 days	20 January 2021	74 years 214 days
Biden	20 November 1942	3 November 2020	77 years 349 days	20 January 2021	78 years 61 days

Before Reagan, the oldest US President to take office was William Henry Harrison (inaugurated in 1773 as the 9th president), at 68 years 23 days. But Harrison died only one month (31 days) into his term; before Reagan, the oldest president at the end of his term was Dwight D. Eisenhower at 70 years, 98 days.

Before Eisenhower, the oldest US President at the end of his term was Andrew Jackson, the 7th president (1829-37), who was aged 69 years and 354 days when he left office.

Donald Trump was the oldest US President to be elected and the oldest to be sworn in, before Joe Biden. But as he only served one term (to date ... ), he was more than three years younger than Reagan when he left office.

Ronald Reagan was sworn in 17 days before his 70th birthday, and left office 17 days before his 78th. On the day of the 2020 election, Joe Biden was exactly the same age as Reagan was when he left office.

If (as seems entirely likely, at the time of writing) Donald Trump stands for re–election in 2024, he will be some five months older than Joe Biden was in 2020.