Gray Wave
According to research by Warren Sanderson et al., (”The coming acceleration of global population ageing“), the mean age of the world population is 30, with 44 years left to live on average. By the end of the century, the mean age is expected to be 45, with 41 years left. So both measures, mean age and average years of life remaining, show aging.
In North America, the average age will go up through the end of the century, (from 37 to nearly 50), but the average years remaining also will go up (from 43 to 48). North America is the only region to show that pattern.
The increase in average age is caused by people living longer, and also fewer babies being born.
As longevity has increased, people have invested more in education (presumably since they’ll have more time to reap the benefits).
The researchers’ model shows an 88% probability that world population growth will end before the end of the century.