Maximum, as opposed to minimum, ages for heads of state are rare, but apparently they do exist. One source states that "We find only one country, Benin, where there is a maximum age of eligibility, set at 70 years for presidential candidates..." https://books.google.com/books?id=IHA8h0QrAZwC&pg=PA55
However, Russia also used to have one: "There is no upper age limit, as there was when the presidency was introduced in 1991. Then there was no residency requirement but a maximum age of 65. Boris Yel'tsin, the first Russian President, was born in 1931, and would have already reached 65 at the latest date for his possible re-election, which was July 1996. No surprise, then, that the upper age limit was eliminated with the reorganisation of the conditions for candidacy for the presidency under the 1993 Constitution..." https://books.google.com/books?id=GIB6BAAAQBAJ&pg=PT85
Challenge: Get such a maximum age limit in the US Constitution.
(This could go in either the pre-1900 or post-1900 section, depending on whether the maximum is found in the original Constitution, a pre-1900 amendment, or a post-1900 amendment. The most likely POD for an amendment is a bad experience with an elderly president who is seen to have been in his dotage. No, I don't mean Reagan, and in any event the 25th Amendment at least in theory provides a way to deal with a senile president.)
However, Russia also used to have one: "There is no upper age limit, as there was when the presidency was introduced in 1991. Then there was no residency requirement but a maximum age of 65. Boris Yel'tsin, the first Russian President, was born in 1931, and would have already reached 65 at the latest date for his possible re-election, which was July 1996. No surprise, then, that the upper age limit was eliminated with the reorganisation of the conditions for candidacy for the presidency under the 1993 Constitution..." https://books.google.com/books?id=GIB6BAAAQBAJ&pg=PT85
Challenge: Get such a maximum age limit in the US Constitution.
(This could go in either the pre-1900 or post-1900 section, depending on whether the maximum is found in the original Constitution, a pre-1900 amendment, or a post-1900 amendment. The most likely POD for an amendment is a bad experience with an elderly president who is seen to have been in his dotage. No, I don't mean Reagan, and in any event the 25th Amendment at least in theory provides a way to deal with a senile president.)