Theodore Roosevelt - Became President at 42
John F. Kennedy - Elected at 43, the youngest to be voted into office.
Bill Clinton - Inaugurated at 46 years old.
Ulysses S. Grant - Assumed office at 46
Barack Obama - Became President at 47
Grover Cleveland - First term began at 47
Franklin Pierce - Took office at 48
James A. Garfield - Inaugurated at 49 & 105 days, sadly assassinated a few months into presidency.
James K. Polk - Became President at 49 & 122 days.
Millard Fillmore - Took office at 50
Check out the List Of Oldest Presidents Elected