Longer life is an achievement. An aging society gets into trouble when too few children grow up beneath its older generations. Low fertility changes the balance between age cohorts.
The familiar population pyramid once had a wide base of children and narrowed toward old age. In a low-fertility country it becomes a column and then begins to turn upside down. The large generation moves into retirement. Smaller cohorts follow it into work and school.
The previous chapter explained the momentum behind this change. Its human meaning is easier to see in an ordinary family. Four grandparents may have two adult children and one grandchild—the “4-2-1” shape associated with China, though the arithmetic appears anywhere one-child families persist. The grandchild won’t care for six older relatives alone. Other relatives and public programs share the burden. The family has nevertheless thinned sideways, leaving fewer people to call when care becomes personal.
Counting support, not birthdays
The old-age dependency ratio compares people above a conventional retirement age with people of conventional working age. Across the OECD, there were 33 people age sixty-five or older for every hundred people ages twenty to sixty-four in 2025. The organization projects 52 by 2050. Korea faces the sharpest turn.
Sixty-five is an administrative boundary rather than a biological one. A healthy seventy-year-old running a business may also watch her grandchildren each week. Counting her as dependent obscures what she provides. Some eighty-year-olds retain capacities comparable to much younger adults; others need substantial support. The World Health Organization therefore defines healthy aging through functional ability.
Health can soften demographic aging considerably. If people remain independent for more of their longer lives, retirement can move later and intensive care can be concentrated near the end. Across OECD countries, life expectancy at sixty-five rose by six years between 1970 and 2023. Those additional years are a gift when an older person can keep doing meaningful work and remain close to family.
Some of the added years will include poor health. WHO reports that the proportion of life spent in good health has remained broadly constant globally, so longer lives have also brought additional years of limitation. Countries vary greatly. Demographers call it a compression of morbidity when serious illness is pushed into a shorter period near death; an expansion means more years lived with disabling conditions.
Low fertility makes the difference more consequential. A larger healthy older population can provide work and care. A larger frail population needs both, just as the pool of younger adults available to supply them narrows. Medicine may add years to life faster than it adds nurses to a ward.
The oldest old
Population aging has stages. The first brings more people in their sixties and seventies, many of whom remain independent. Later, the population over eighty grows rapidly and daily help becomes more common. The OECD projects Korea’s share over eighty to rise from 4.4 percent in 2023 to 16.5 percent in 2050. That creates a different care economy, not simply a larger retirement class.
Fixed age ratios can therefore exaggerate one problem and miss another. They count a productive sixty-six-year-old as dependent while treating a fifty-nine-year-old with a severe disability as a supporter. They also flatten the enormous difference between supporting pensions for active retirees and providing round-the-clock care for the oldest old.
Better measures should count health and employment alongside chronological age. Governments can raise retirement ages as lives lengthen, while employers make work possible for older bodies. Families also need help before caring for a parent consumes the caregiver’s own health.
These adaptations are worth making even if fertility recovers tomorrow, because the people who will be old in 2050 are already alive. Healthy longevity can turn some additional years from dependency into contribution. The caregivers missing from small birth cohorts remain missing. One generation can adjust the boundary between work and retirement. Five generations of contraction change how many people stand on either side of it.
Citations
- Organisation for Economic Co-operation and Development, “Rapidly ageing populations will continue to put pressure on pension systems”, November 27, 2025.
- World Health Organization, “Healthy ageing and functional ability”, 2020.
- Organisation for Economic Co-operation and Development, “Life expectancy and healthy life expectancy at older ages”, in Health at a Glance 2025, 2025.
- World Health Organization, “Ageing and health”, 2025.
- Organisation for Economic Co-operation and Development, “Demographic trends”, in Health at a Glance 2025, 2025.