The median age upon accession to the presidency is 55 years and 3 months . This is how old Lyndon B. Johnson was at the time of his inauguration . The youngest person to assume the office was Theodore Roosevelt , who became president at the age of 42 years , 322 days , following William McKinley 's assassination ; the oldest was Donald Trump , who was 70 years , 220 days old at his inauguration . The youngest person to be elected president was John F. Kennedy , at 43 years , 163 days of age on election day ; the oldest was Ronald Reagan , who was 73 years , 274 days old at the time of his election to a second term .

Question: who was the oldest man elected president of usa
Answer: Ronald Reagan