The median age upon accession to the presidency is roughly 55 years and 6 months, which is about how old Benjamin Harrison was at the time of his inauguration. The youngest person to assume the office was Theodore Roosevelt, who became president following William McKinley 's assassination, at the age of 7004156620000000000 ♠ 42 years, 322 days. The youngest person elected president was John F. Kennedy, who was inaugurated into office at the age of 7004159420000000000 ♠ 43 years, 236 days. Assassinated three years into his term, he became the youngest at the time of leaving office (7004169780000000000 ♠ 46 years, 177 days); the youngest person at the time of leaving office after serving a full four - year term was Theodore Roosevelt (7004183900000000000 ♠ 50 years, 128 days). The oldest person at the time of entering office was Donald Trump, at the age of 7004257880000000000 ♠ 70 years, 220 days; Ronald Reagan was the oldest person in office, at the age of 7004284730000000000 ♠ 77 years, 349 days when his presidency ended in January 1989.
who is the oldest elected united states president
Donald Trump