* Over 25 percent of the world's population is less than 15 years old. The figure is 41 percent in least developed countries and 16 percent in more developed countries.
* Japan has the oldest population profile, with over a quarter of its citizens older than 65. Qatar and the United Arab Emirates are at the other end of the spectrum, with each having only 1 percent over 65.
* The top 10 fertility rates in the world are in sub-Saharan African countries, with nearly all above six children per woman, and one topping seven. In Europe, the average is 1.6.
* The fertility rate in the United States is 1.8 children per woman, down from 1.9 in 2014. “Replacement” fertility in the United States—that is, the rate at which the population exactly replaces itself from one generation to the next, excluding the effects of migration—is 2.1 children per woman.
* Thirty-three countries in Europe and Asia already have more people over age 65 than under 15.You can see that fertility rates, and the changing age structures they bring about, remain key factors in the world's demographic picture.