Suppose Jimmy Carter was elected President in 1992 instead of Bill Clinton.
Carter was 68 years old in 1992 and is still active today.
There are two possible PODs. The most likely is that Carter does not run for President in 1976 or runs but loses. He then gets elected to the Senate in 1978 and does run for President successfully in 1992. The problem with this timeline is that it completely butterflies away the OTL Carter administration -and also Sam Nunn's senatorial career- so by the time 1992 comes around things are already completely different.
The more interesting POD, that keeps everything the same up to 1992, is a Carter political comeback. By 1992 Carter had improved his reputation with the public that a comeback was feasible. Carter seems to have had no interest in doing this, he also could have been elected to the Senate from Georgia in 1986 or returned as Governor and passed that up (Georgia elected a Democrat to the Senate in 1986 and Carter carried the state in 1980 so I think that seat could have been Carter's if he had wanted it). But if George McGovern could run for president again in 1988, a Carter comeback is not a crazy idea and lets say he goes for it and it actually works.