The group's population is expected to reach 1.53 billion by the year 2050, three times more than the 516 million alive today. By mid-century, 16 percent of the world's population is expected to be 65 or older.
In the United States, the size of the group is expected to rise to more than double the current amount, expanding from 39 million in 2009 to 89 million by 2050.
The report also predicts that the 85-and-older group will increase from 40 million in 2009 in the world to 219 million by mid-century.
According to the press release, 20 percent or more of the population in Germany, Italy, Japan and Monaco are 65 years or older. By 2050, 100 countries will have an older population accounting for 20 percent or more of their country, with Europe remaining the world's oldest region.
While the world's children are estimated to still outnumber the old over the next 50 years, the population of 15 and under will most likely fall behind, increasing by only 6 percent during the same period, from 1.83 billion to 1.93 billion. The 15 and under population in the U.S. is projected to increase from current 62 million to just 85 million.
Sub-Saharn Africa is expected to remain the youngest region in the world due to higher fertility rates and the spread of HIV/AIDS, with only 5 percent of the population being 65 and older by 2050.
"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, in the report.
China and India, the world's most populous countries, have the largest number of seniors, though the percentages of the population is less. Currently China's 65-and-older population is at 109 million and India's at 62 million. They are expected to rise to 350 million and 240 million, respectively, by 2050.
For more information, you can check out the Census Bureau's International Data Base which has demographic indicators for countries and areas of the world with populations of 5,000 or more.