Youngest elected as US president

John F. Kennedy (b. 29 May 1917; d. 22 November 1963), Democratic victor in the 1960 US presidential election, was 43 years 236 days old at his inauguration on 20 January 1961.

Kennedy was the youngest man ever to have been elected president, but Theodore Roosevelt (b. 27 October 1858; d. 6 January 1919) succeeded to the US presidency on 14 September 1901 at the age of 42 years 322 days, after the assassination of of his predecessor, William McKinley.