You have to be at least 35 years old to be the president of the United States — it's been the same since the Constitution was written in 1787. And while no president has ever been that young, Theodore Roosevelt came pretty close.
VP Roosevelt Assumed Office
Roosevelt became the 26th president of the United States in 1901 after the assassination of President William McKinley. Roosevelt was 42 at the time, and stepped into the presidency because he was vice president. How he got this job in the first place is a little bit of a story in itself.
Roosevelt became interested in politics very early in life, and at 23 was elected to the New York State Assembly — the youngest person ever elected to that office. After serving in various appointed government positions, becoming a cattle rancher in the Dakota Territory for a while and then a war hero in Cuba, he ran for and won the race for governor of New York in 1898 at the tender age of 40.
In 1899, William McKinley's vice president Garret Hobart died of heart failure. Roosevelt was nominated to be McKinley's running mate at the 1900 Republican National Convention, and secured their victory with a whirlwind campaign tour of 480 stops in 23 states.
He served as vice president for only six months before President McKinley was shot and killed while making his way to the podium to make a speech at the Pan-American Exposition, a World's Fair held in Buffalo, New York in 1901. Roosevelt assumed office only about a month before his 43rd birthday.
Kennedy Was Elected
On Nov. 22, 1963, when he was just barely past his first 1,000 days in office, JFK was assassinated in Dallas, Texas, also becoming the youngest president to die in office.