When President Biden assumed office, he was 78 years old, older than Ronald Reagan when he left office, and 22 years older than the median age of a POTUS since 1960.
Of the 45 individuals who have served as president, 6 have chosen not to run for reelection to a 2nd full term: LBJ, James Polk, James Buchanan, Rutherford B. Hayes, Calvin Coolidge, and Harry S. Truman.