Age mix varies by region. In the more developed countries of the world, the number of old people will steadily increase, and the number of children will decline (Exhibit 4). By 2015, old people will outnumber children; this has already occurred in several countries, including Japan and Germany. By 2010, the working-age population will begin shrinking; by 2035, total population will begin shrinking. In contrast, the less developed countries will face large increases in their working-age populations, a quadrupling of their old populations, and only a slight decrease in their number of children.

The share of old people will increase sharply. The pace of aging will accelerate globally. In the more developed countries, old people already make up 15% of the population and will increase to 26% by 2050. Japan and Italy, which currently have the world’s oldest populations, with nearly 20% of their populations 65+, will see steep increases to more than 30%. Due to a precipitous drop in fertility following World War II, Japan is one of the most rapidly aging countries, and by 2050, 38% of its population will be 65+.

The United States, with only 12% of its population currently age 65+, is “young” relative to the other advanced economies and will remain so despite aging of the baby boomers. The U.S. proportion of people 65+ will start increasing around 2010, when the first boomers reach 65, but will level off at around 20% after the last boomers turn 65 (Exhibit 5).

In contrast to the already aging populations in the advanced economies, population aging in the less developed countries is just beginning and will sharply accelerate after 2015, reflecting the impact of fertility declines that occurred in the late 1960s and early 1970s. In the less developed countries, the share of people 65+ will almost triple, from 5.5% in 2005 to 15% in 2050.

South Korea, one of the most rapidly aging countries, has already seen its share of people age 65+ increase from 5% to more than 9% over the last 15 years. With an increase to 35% projected for 2050, South Korea will then replace Italy as the world’s second-oldest country. In many countries, including China and Mexico, the pace of aging accelerates especially sharply after 2015, reflecting the steep fertility declines and its share of people age 65+ increasing from 8% to 20% in just 30 years, will age nearly three times faster than that of the United States, where the same increase will occur over about 85 years.

By 2050, the less developed countries, with a 15% share of 65+, will have populations as old as the more developed countries have today. The rapid pace of aging in the less developed countries will require them to adjust much faster than has been necessary in more developed countries. Moreover, the sheer size of the population will make their adjustments even more challenging. The numbers are staggering: The population of age 65 and older in less developed countries will quadruple, from 300 million in 2005 to 1.2 billion by2050.

Median age is increasing rapidly. Median age provides another useful perspective on how the age distribution is shifting. Globally, median age—the age at which half the population is younger and half is older—is projected to increase from 28 years in 2005 to 38 years by 2050.

Many rapidly aging Asian countries face especially steep increases in median age, owing to their early fertility declines. China’s population, with a current median age of 33, is about ten years older than the populations of other developing countries. South Korea is even older and faces a more accelerated increase in median age. By 2050, median age will have increased 12 years to 45 in China and 20 years to 55 in South Korea.

Mexico will also age rapidly, largely due to a projected 31% decline in the number of children over the next 45 years. By 2050, half of Mexico’s population will be older than 43, an 18-year increase in median age. Other rapidly aging countries that will have large gains in median age include Iran, Mongolia, and Vietnam. In contrast, many “young” countries, such as those in sub-Saharan Africa, will show little increase in median age. The projected median age in 2050 for all less developed countries is 37, up from 26 in 2005.

Although less developed countries are projected to gain 11 years in median age by 2050, aging in the older, more developed countries will generally be more gradual, with an average gain of 7 years. Two exceptions are Japan, with a projected 12-year gain, and Spain, with an 11-year gain. As previously noted, aging in the United States will be more gradual, with the median age increasing only 5 years, from today’s 36 years to 41 in 2050 (Exhibit7).

Excerpted from Hayutin, Adele (2007).Global demographic shifts create challenges and opportunities. PREA Quarterly (Fall), 46–53. For the full article, see click here.