The world's 65-and-older population is projected to triple by mid-century, from 516 million in 2009 to 1.53 billion in 2050, according to the U.S. Census Bureau. In contrast, the population under 15 is expected to increase by only 6 percent during the same period, from 1.83 billion to 1.93 billion.

In the United States, the population 65 and older will more than double by 2050, rising from 39 million today to 89 million. While children are projected to still outnumber the older population worldwide in 2050, the under 15 population in the United States is expected to fall below the older population by that date, increasing from 62 million today to 85 million.

These figures come from the world population estimates and projections released today through the Census Bureau's International Data Base. This latest update includes projections by age, including people 100 and older, for 227 countries and areas.

Less than 8 percent of the world's population is 65 and older. By 2030, the world's population 65 and older is expected to reach 12 percent, and by 2050, that share is expected to grow to 16 percent.

"This shift in the age structure of the world's population poses challenges to society, families, businesses, health care providers and policymakers to meet the needs of aging individuals," said Wan He, demographer in the Census Bureau's Population Division.

From 2009 to 2050, the world's 85 and older population is projected to increase more than fivefold, from 40 million to 219 million. Because women generally live longer than men, they account for slightly more than half of the older population and represent nearly two-thirds of the 85 and older population.

Europe likely will continue to be the oldest region in the world: by 2050, 29 percent of its total population is projected to be 65 and older. On the other hand, sub-Saharan Africa is expected to remain the youngest region as a result of relatively higher fertility and, in some nations, the impact of HIV/AIDS. Only 5 percent of Africa's population is projected to be 65 and older in 2050.

Countries experiencing relatively rapid declines in fertility combined with longer life spans will face increasingly older populations. These countries will see the highest growth rates in their older populations over the next 40 years.

There are four countries with 20 percent or more of their population 65 and older: Germany, Italy, Japan and Monaco. By 2030, 55 countries are expected to have at least one-in-five of their total population in this age category; by 2050, the number of countries could rise to more than 100.

Although China and India are the world's most populous countries, their older populations do not represent large percentages of their total populations today. However, these countries do have the largest number of older people - 109 million and 62 million, respectively. Both countries are projected to undergo more rapid aging, and by 2050, will have about 350 million and 240 million people 65 and older, respectively.

The International Data Base offers a variety of demographic indicators for countries and areas of the world with populations of 5,000 or more. It provides information on population size and growth, age and sex composition, mortality, fertility and net migration.