Tyler Cowen cites a study that says that the rate at which life expectancy at birth (LEB) is increasing has slowed down. This does not surprise me.
Suppose that there are two outcomes. One outcome is that you live to a ripe old age. The other outcome is that you die within one year of birth. As the percentage of people who die early goes from 10 percent to 1 percent, average LEB goes up dramatically. As it goes from 1 percent to 0.1 percent, average LEB goes up more slowly. But I would not call that stagnation.