James K. Polk had the shortest retirement of any president, dying barely three months after leaving office at age 53 (the youngest president to die of natural causes). Jimmy Carter's retirement, now 40 years, is the longest in American presidential history. At age 96, Jimmy Carter is also the oldest living president as well as the nation's longest-lived president. The youngest living president is Barack Obama, age 59. Altogether, six U.S. presidents have lived into their 90s. The first to do so, John Adams, was the longest-lived president for nearly two centuries, from 1803 until Ronald Reagan surpassed his lifespan, in October 2001. The six presidents, arranged by lifespan are: