In fact, going by the year of birth, only once in the last century have Americans elected a president older than the sitting occupant of the White House – in 1980, the people voted for Ronald Reagan who was 13 years older than President Jimmy Carter. There are much smaller differences than that, of course, and much larger ones as well – John F. Kennedy was 27 years younger than Dwight D. Eisenhower. But as you can see in this chart, the larger trend holds.

In some ways this may not be a surprise. Elections are about the future, not the past. In most cases “new ideas” are seen as an attribute and youth and vigor are seen as essential for the most demanding job in the world.

And yet, where 2016 is concerned, if Ms. Clinton, the presumed Democratic front-runner, were to win the White House, the age gap between her and Mr. Obama (+14 years) would be larger than the gap between Presidents Jimmy Carter and Ronald Reagan (+13 years).

For Mr. Bush, a presumed front-runner for the GOP, the gap is smaller, but still significant at +8 years.