Who was the youngest President-elect at the time of his inauguration?
At 43 years, 236 days, John F. Kennedy was the youngest President-elect. Teddy Roosevelt was 42 years, 322 days old when he was sworn in following the death of President McKinley.
John F. Kennedy is sworn in by Chief Justice Earl Warren.
It is not required that the Chief Justice of the United States administer the Presidential oath. Seven Presidents were not sworn in by the Chief Justice. They were George Washington, John Tyler, Millard Fillmore, Chester Alan Arthur, Theodore Roosevelt, Calvin Coolidge, and Lyndon Baines Johnson.