Nothing is immortal, of course, save the heavens and the earth. And truth be told, scientists tell us even the stars and the planets have expiration dates. But their demise is inconceivably distant. Think billions of years. So, go ahead and plan next year’s vacation. The odds of Yellowstone National Park still being there are excellent.

For humankind, however, the time scale of our lives is a relative blink of the eye. The average American’s lifespan is about 77 years.

How far might science further extend our lives?

A new study suggests humanity is very close to the limits of human aging. The average lifespan is no longer growing significantly in the developed world and, the study says, significant increases in average age are unlikely.

Beyond a certain age, and even with medical advances, curing one disease simply means another will claim its spot. We cannot reverse cellular aging ­— yet.

Scientists examined population data from the eight nations with, on average, the longest living people, plus the U.S.

France, Italy, Japan, Sweden, and Switzerland are on the list. Data show jumps in average lifespan have slowed since 1990.

The study predicts that over the next three decades, humans are likely to gain no more than 2.5 years.

Our main risk factors for death now are related to biological aging, the accumulated damage over time to cells and tissues. There is hope that some future gene therapy could reverse cell aging. A Harvard scientist contends that the first person who will live 150 years has already been born.

Of course, this young Methuselah doesn’t know that.