Donald Trump (born June 14, 1946) is the oldest person to take office as President of the United States. On January 20, 2017 (inauguration day), he was 70 years and 220 days old.

Ronald Reagan (born February 6, 1911) was 69 years and 349 days old on January 20, 1981 (inauguration day).

James Buchanan (born April 23, 1791) was 65 years and 315 days old on March 4, 1857 (inauguration day).

William Harrison (born February 9, 1773) was 68 years and 23 days old on March 4, 1841 (inauguration day).

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