Ageing should be based on the number of years people are likely to live in a given country in the 21st century, say researchers. By that logic, 70 may be the new 60.

The new study also predicts an end to population aging in the United States and other countries before the end of the century.

Population ageing—when the median age rises in a country because of increasing life expectancy and lower fertility rates—is a concern for countries because of the perception that population ageing leads to declining numbers of working age people and additional social burdens.

“This study is different from previous research in that we used United Nations forecasts that take uncertainty into account and combine those forecasts with our new measures of ageing,” says Warren Sanderson, professor of economics at Stony Brook University and the lead author of the study in PLOS ONE.

Image: World Health Organization

“When this is done, it is a virtual certainty that population aging will come to an end in China, Germany, and the US well before the end of the century.”

Sanderson emphasizes that the projections imply that as life expectancies increase people are generally healthier with better cognition at older ages and countries can adjust public policies appropriately as to population aging.

Population ageing could peak by 2040 in Germany and by 2070 in China, according to the study, which combines measures of ageing with probabilistic population projections from the UN. In the United States, the study shows very little population ageing at all in the coming century.

Traditional population projections categorize “old age” as a simple cutoff at age 65. But as life expectancies have increased, so too have the years that people remain healthy, active, and productive. In the last decade, International Institute for Applied Systems Analysis researchers have published a large body of research showing that the very boundary of “old age” should shift with changes in life expectancy, and have introduced new measures of ageing that are based on population characteristics, giving a more comprehensive view of population ageing.

The study combines these new measures with UN probabilistic population projections to produce a new set of age structure projections for four countries: China, Germany, Iran, and the United States.

“Both of these demographic techniques are relatively new, and together they give us a very different, and more nuanced picture of what the future of aging might look like,” adds Sanderson, also a researcher at IIASA.

One of the measures used in the paper looks at life expectancy as well as years lived to adjust the definition of old age. Probabilistic projections produce a range of thousands of potential scenarios, so that they can show a range of possibilities of aging outcomes.

For China, Germany, and the United States, the study shows that population aging would peak and begin declining well before the end of the century. Iran, which had an extremely rapid fall in fertility rate in the last 20 years, has an unstable age distribution and the results for the country were highly uncertain.

“We chose these four countries for analysis because they have very different population structures and projections, and so they allow us to test this methodology across a range of possible scenarios,” summarizes study coauthor Sergei Scherbov, leader of the Re-Ageing Project at IIASA.

Patrick Gerland, chief of the mortality section of the Population Division of the UN is also a coauthor of the paper.

The European Research Council under the European Union’s Seventh Framework Programme, contributed to the funding of the research. The Population Division of the United Nations provided the researchers with access to data from the World Population Prospects: The 2015 Revision.