We have just seen the end of the fourth time in American history that we have had six living Presidents.
The first time was in 1861-1862, from March to January, a total of about 10 and a half months, when we had President Abraham Lincoln, and former Presidents Martin Van Buren, John Tyler, Millard Fillmore, Franklin Pierce, and James Buchanan, until John Tyler died in January 1862.
The second time was 1993-1994 from January to April, a total of about 15 months, when we had President Bill Clinton, and former Presidents Richard Nixon, Gerald Ford, Jimmy Carter, Ronald Reagan and George H. W. Bush, until Richard Nixon died in April 1994.
The third time, the longest time, was 2001-2004, from January to June, a total of about 40 and a half months, when we had President George W. Bush, and former Presidents Gerald Ford, Jimmy Carter, Ronald Reagan, George H. W. Bush, and Bill Clinton, until Ronald Reagan died in in June 2004.
And now, the fourth and last time, was 2017-2018, from January to November, a total of about 22 and a half months, the second longest time, when we had President Donald Trump, and former Presidents Jimmy Carter, George H. W. Bush, Bill Clinton, George W. Bush, and Barack Obama, until George H. W. Bush died on the last day of November 2018.
The odds of having a fifth period of six Presidents anytime soon seems unlikely, as Jimmy Carter, at age 94, would seem unlikely to have much more life longevity, but if Donald Trump were to be forced out of office, in the next two years, or be defeated, and Carter stayed in good health, it could happen.