1. Theodore Roosevelt Age at inauguration: 42 years, 322 days In office: 1901–1909 The youngest President assumed the position when he was Vice-president, after President William McKinley was assassinated. Roosevelt was then re-elected, in the Election of 1904. No fan of wealthy tycoons, Roosevelt made a name for himself as a “trust buster,” opposing collaborations of big businesses. A war hero (for his actions during the Spanish-American War), Roosevelt won the Nobel Peace Prize for negotiating the end of the Russo-Japanese War, in 1905. TR, as he was also known, was also a prime mover in the drive to build the Panama Canal. A nature lover, Roosevelt dramatically expanded the size and number of America’s national parks.