Key Themes in Research on the Demography of Aging

Population aging is unquestionably the most important demographic force of the first half of the twenty-first century. As a result of declines in fertility and dramatic improvements in mortality in many countries and regions of the world, the world's population is growing older. Moreover, the rate at which this is occurring is unprecedented in human history. The share of the world's population aged 65 or older is expected to nearly double between 2008 and 2040, from 7.8% to 14.7%. In addition, the number of older people will increase by a factor of 2.5 during this same period, from 530 million in 2010 to 1.3 billion by 2040.¹

Population aging is a global phenomenon, but the timing and dynamics of aging differ substantially across countries. Developing countries are experiencing the fastest rates of population aging. A common measure of the rate of population aging is the number of years it will take for the percentage of a population who are aged 65 or older to double. In several countries in Asia and Latin America, the pace of aging is extremely rapid. South Korea is experiencing the most rapid rate of aging, where the percentage aged 65 and older is expected to double from 7% to 14% within 18 years (2000-2018).

In contrast, developed countries experienced population aging earlier, and at a relatively slow rate, throughout the second half of the twentieth century. The same doubling of the population aged 65 and older that will occur within 18 years in South Korea happened over a much longer period of time in most of Western Europe, Australia, the United States, and Canada. For example, it took more than a century (1865-1980) for France and 85 years (1890-1975) for Sweden to experience this same increase. Despite the slower progression of aging in developed countries, however, the aging of the baby boom generation will lead to unprecedented numbers and percentages of persons at older ages in many countries within the next decade.

Another aspect of population aging that has gained increasing importance is the aging of the older population itself. The share of the older population at ages 80 and older (often referred to as the oldest-old) is growing more rapidly than the older population itself—worldwide, the growth rates for 1999-2000 were 3.5% for those aged 80 and older compared with 2.3% for those aged 65 and older. This growth will translate into a large increase in the share of oldest-old within the world's older population, from 16% in 2000 to 24% in 2040. Again, there is considerable variation across countries. Japan, which currently has the oldest population in the world (21.6% are aged 65 or older), is also experiencing the most rapid aging of its older population. By 2040, 38% of the population aged 65 or older will be aged 80 or older, up from 22% in 2000. In many developing countries where mortality is still relatively high, these percentages are much lower, though the rate of growth of the oldest-old is still very high (Hermalin 2000).

While the demographic forces that underlie population aging (mainly fertility and mortality rates) are well understood and generally predictable, what is less predictable is how these forces will interact with social and economic changes and cultural influences to shape the aging experience. In most respects, population aging is a great success story. One important underlying factor is the increase in longevity that has occurred over the past half-century, which is due in large part to the eradication of infectious diseases and effective treatment and management of chronic diseases. As a result of these advances, people born in 2010 can expect to live until age 69 worldwide on average, 17 years longer than those born 50 years earlier (United Nations 2009). Furthermore, individuals who reach age 65 can expect to live an additional 16 years on average (World Health Organization 2010). On balance, this means that older adults will have more time to enjoy their retirement...