The U.S. population of people who are 90 or older was 1.9 million in 2010, nearly triple what it was three decades ago, according to a recent U.S. Census Bureau report. The findings, supported by the National Institute on Aging, also showed that over the next four decades, that population is expected to more than quadruple.

The aging population means the country will have a greater need for students who are enrolled in online nursing degree programs, as people older than 65 need about four times as much medical attention as younger people, the American Association of Colleges and Nursing said.

Thanks to advancing medicine, life expectancies are growing, and people 90 and older now make up 4.7 percent of the population older than 65, compared with 2.8 percent in 1980. The report said that by 2050, that is expected to jump to 10 percent.

"Traditionally, the cutoff age for what is considered the 'oldest old' has been age 85," said Census Bureau demographer Wan He. "But increasingly, people are living longer and the older population itself is getting older. Given its rapid growth, the 90-and-older population merits a closer look."