Who was the youngest president of the United States?

Teddy Roosevelt was our youngest president at 42 when he took office after William McKinley was assassinated.

John F. Kennedy was the youngest elected president at the age of 43.

BTW, Ronald Reagan was the oldest elected president at 69.

This is correct.

Meant as a footnote only...

Several men served as President of the United States under the Articles of Confederation. Among them was "Mr. Signature" himself, John Hancock, who served as both its 3rd and 7th President. BOrn on January 23, 1737, his first term began on May 24, 1775 at age 38.

Atta boy, Fuse !