When I was born, there were no living ex-Presidents. Nixon had yet to resign. Kennedy, Hoover, and Eisenhower had died in the 60s, and then Truman and LBJ had died within a month of each other in 1972 and 1973. But then there was not another Presidential death until Nixon's in 1994 when I was 20. In the meantime, the ranks of living ex-Presidents had grown from zero to five: Nixon, Ford, Carter, Reagan, and George Bush I. You'll remember that Robert Smigel made a pretty funny cartoon about it.
You should not be surprised to learn that one can see this information in convenient tabular form on Wikipedia. It turns out that there were previously periods of no living ex-Presidents during the administrations of George Washington (obviously), John Adams, U.S. Grant, Teddy Roosevelt, and Herbert Hoover. There have never been more than five living ex-Presidents, but it has happened three times:
- March 4, 1861 to January 18, 1862, during Abraham Lincoln's administration: Van Buren, Tyler, Fillmore, Pierce, and Buchanan;
- January 20, 1993 to April 22, 1994, during Bill Clinton's administration: Nixon, Ford, Carter, Reagan, and the first George Bush; and
- January 20, 2001 to June 5, 2004, during George Bush the Less's administration: Ford, Carter, Reagan, Bush's dad, and Clinton.
Wikipedia comes in handy again, this time with a timeline. They don't tally things up for us, but if you go through and add things up, you can figure out that there were four periods of time when there were 18 men living who at some point in time had or would become President of the United States:
- October 4, 1822 to July 4, 1826, Rutherford B. Hayes' birth to the deaths of John Adams and Thomas Jefferson;
- August 20, 1833 to June 28, 1836, Benjamin Harrison's birth to James Madison's death;
- March 18, 1837 to April 4, 1841, Grover Cleveland's birth to William Henry Harrison's death in office; and
- January 29, 1843 to June 8, 1845, William McKinley's birth to Andrew Jackson's death.
*This is one of the most remarkable Presidential trivia tidbits: founding fathers John Adams and Thomas Jefferson died within five hours of each other on July 4, 1826, the 50th anniversary of the Declaration of Independence.