Zer0 was 47 years, Kennedy was 43 years, Theodore Roosevelt was 40 years, Grover Cleveland was 47 years, and Ulysses S. Grant was 46 years,
If Rubio were elected, he would be 45 on inauguration day—less than a year younger than Bill Clinton was when he became President, or, for that matter, less than a year younger than Ulysses S. Grant was when he became President. To be sure, Grant had a more impressive resume.