At the end of the 20th century, only two U.S. presidents in history had reached 90 years of age, in far different eras at that.  By the start of 2014, this number had risen to four, then a few months ago to five, and today the total hits six.  Remarkable all the more are four in a row; that is, the four additional nonagenarian commanders-in-chief of the 21st century held office consecutively.

While what’s called “the world’s hardest job” clearly ages the incumbent, it doesn’t seem to be shortening his lifespan these days.  Then again, it’s worth noting that all but one of these multi-party six were one-termers.  Furthermore, this distinction won’t see number seven for quite a while yet.

How’s all this for a could-be Jeopardy! category of presidential longevity?

Jimmy Carter turns 90 today, in addition to the post-presidential record he set two years ago. (Photo: AJC/Curtis Compton)