If we go by U.S. Census Bureau projections for Japan, for example, there will be so many people over 100 years of age in 2040, and so few babies, that there could almost be one centenarian on hand to welcome each Japanese newborn.
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Consider, for example, a woman born in 1990, now 22 years old. Given current trends, the institute estimates her life expectancy to be around 90, maybe higher. But children—and family, at least in the current understanding of the term—may very well not be part of her life experience. The projections give her slightly less than even odds of getting married, and staying married to age 50. Her chances of never marrying at all are nearly one in four. Further, these projections suggest she has nearly a two-fifths (38 percent) chance of ending up childless. Even more astonishing: She has a better-than-even chance of completing life with no biological grandchildren.