The U.S. presidency is a geezer’s game this round.

If Donald Trump wins and completes a full term he'd be 78, while a President Joe Biden would be 82 -- thus the unusually intense buzz about Sen. Kamala Harris as president in waiting. Either man would be history’s oldest president.

On the religion beat, Pope Francis appears spry but he turns 84 in December and, inevitably, writers are already starting to muse about his successor. An election campaign for the leader of 1.3 billion Catholics is the religion writer’s equivalent of the Olympics, compounded by secrecy and subtlety. This should be an unusually hot race because Francis has roiled conservatives on both doctrinal and political matters.

Francis’s dozens of appointees to the College of Cardinals will exercise major voting power in the coming “conclave,” but that doesn’t mean his successor will be a clone. Cardinals chosen by the doctrinaire St. John Paul II and Benedict XVI, after all, elected Francis. (As religion specialists will know, only cardinals under age 80 are electors and their total cannot exceed 120, with a two-thirds majority required to win.)

Further on the age factor. Some will say the rule of thumb has moved to older popes, as with the U.S. presidency, since both Francis and predecessor Benedict XVI were in their later 70s when chosen. However, back in 1958 the cardinals elevated a similarly aged Angelo Roncalli, the patriarch of Venice. Some figured he’d be a mere caretaker; in fact, he summoned the epochal Second Vatican Council.

One final age factor. It seems inconceivable that the cardinals would choose a youngster like Pope Pius IX, who was only 54 when elevated and had a turbulent 32-year reign.

By odd coincidence, two conservative Catholic publishers have simultaneously issued relevant pre-conclave books with the identical title, though the subtitles signal different purposes.