For most of U.S. history, children have outnumbered older adults. The Census Bureau now projects this will reverse around 2029, when Americans aged 65+ will exceed those under 18 for the first time. In 1950 there were almost four children per older adult; by 2024 the gap had narrowed to about 12 million. The shift stems from a five-fold rise in the older population (from 12.3 million in 1950 to 61.2 million in 2024) while the number of children stayed near 73 million.

The 2023 Census projections place the crossover five years earlier than the superseded 2017 estimate of 2034, reflecting lower fertility. Eleven states and nearly half of U.S. counties have already crossed this line. Driving forces include the aging baby-boom cohort, rising life expectancy, and sub-replacement fertility.

The change invites two interpretations: as fiscal pressure on Social Security and Medicare, or as a public-health success. The U.S. ages later than many peers, ranking 34th in 2020. The exact year depends on immigration and fertility assumptions, and age thresholds are arbitrary, but the trend is clear.