As of 2017, who has been the youngest American Defense Secretary?

Donald Henry "Don" Rumsfeld (born July 9, 1932) is an American retired politician and businessman. Rumsfeld served as the 13th Secretary of Defense from 1975 to 1977 under President Gerald Ford, and as the 21st Secretary of Defense from 2001 to 2006 under President George W. Bush. He is both the youngest and the second oldest person to have served as Secretary of Defense. Additionally, Rumsfeld was a three-term U.S. Congressman from Illinois (1963–1969), Director of the Office of Economic Opportunity (1969–1970), Counsellor to the President (1969–1973), the United States Permanent Representative to NATO (1973–1974), and White House Chief of Staff (1974–1975).

When Ford lost the 1976 election, Rumsfeld returned to private business life, and was named president and CEO of the pharmaceutical corporation G. D. Searle & Company. He was later named CEO of General Instrument from 1990 to 1993, and chairman of Gilead Sciences from 1997 to 2001.