Joe Biden Turns 78 and Is Set to Become the Oldest US President.br President-elect Biden br turned 78 years old br on Friday, Nov. 20.br When he is sworn in two months from now, Biden will replace Ronald Reagan as the nation's oldest president.br Reagan was 77 years and 349 days old when he left office in 1989.br Biden's physical and mental health have br been a concern for some people.br but in a September interview with CNN, he promised to be "totally transparent" about any health issues if elected president.br His physician, br Dr. Kevin O'Connor, br described Biden as...br “... healthy, vigorous ... fit to br successfully execute the duties br of the Presidency, to include those br as Chief Executive, Head of State br and Commander in Chief.” .