List of presidents of the United States by age
The median age upon accession to the presidency is 55 years and 3 months. This is how old Lyndon B. Johnson was at the time of his inauguration. The youngest person to assume the office was Theodore Roosevelt, who became president at the age of , following William McKinley's assassination; the oldest was Donald Trump, who was old at his inauguration. The youngest person to be elected president was John F. Kennedy, at of age on election day; the oldest was Ronald Reagan, who was old at the time of his election to a second term.
Thomas Jefferson Boynton
Boynton served as the District Attorney for the United States District Court for the Southern District of Florida at Key West from 1861 to 1863. President Abraham Lincoln appointed him (by recess appointment) on October 19, 1863, to the United States District Court for the Southern District of Florida, to the seat vacated by William Marvin. At age 25, he is the youngest federal judge in U.S. history. Nominated on January 5, 1864, he was confirmed by the Senate on January 20, 1864, and received commission on January 20, 1864.