Former President George H. W. Bush marked his 90th birthday yesterday by skydiving from a helicopter. This sort of longevity is seemingly universal among chief executives from the last few decades. Ronald Reagan and Gerald Ford both lived to be 93, and Jimmy Carter is still alive and active at 89.
I have read (although I don't have any relevant links) that modern presidential campaigns are so strenuous that only the most healthy candidates can endure them. It seems reasonable that such a process would select a group of Presidents healthy enough to generally live abnormally long lives.
Presidents from before about forty years ago did not tend to reach such advanced ages, however. Richard Nixon lived to 81, Dwight Eisenhower died at 78, and Lyndon Johnson only made it to 64.
Was this because health care at the time was less advanced, or were campaigns in that era less grueling, and thus less likely to select Presidents with the potential to live to 90?