America aged rapidly in the last decade as baby boomers grew older and births dropped

The United States grew older, faster, last decade.

The share of residents 65 or older grew by more than a third from 2010 to 2020, and at the fastest rate of any decade in 130 years, while the share of children declined, according to new figures from the most recent census.

The declining percentage of children younger than age 5 was particularly noteworthy in the figures from the 2020 head count released Thursday. Combined, the trends mean the median age in the U.S. jumped from 37.2 to 38.8 over the decade.

America's two largest age groups propelled the changes: more baby boomers turning 65 or older and millennials who became adults or pushed further into their 20s and early 30s. Also, fewer children were born between 2010 and 2020, according to numbers from the once-a-decade head count of every U.S. resident.

The decline stems from women delaying having babies until later in life, in many cases to focus on education and careers, according to experts, who noted that birth rates never recovered following the Great Recession of 2007-09.

At the top end of the age spectrum, the number of people older than 100 increased by half, from more than 53,000 people to more than 80,000. The share of men living into old age also jumped. Buddy Lebman, a 98-year-old in the St. Louis area, said the key to longevity is good genes and staying active. He plays bridge twice a week, leads a discussion on current events at his retirement community, and is still involved with his synagogue and a school he helped found. Up until five years ago, he went on regular bicycle rides.

"I just recently had my pacemaker checked out, and the doctor told me it's good for 4 1/2 more years," Lebman said. "So I have to live at least that amount."

People reaching age 100 benefited from a century of vaccines and antibiotic developments, improvements in surgery and better treatment of diseases, said Thomas Perls, a professor of medicine at Boston University.

"Many more people who have the genetic makeup and environmental exposures that increase one's chances of getting to 100, but who would have otherwise died of what are now readily reversible problems, are able to fulfill their survival destiny," Perls said.

The median age varied widely by race and ethnicity. Non-Hispanic whites were the oldest cohort, with a median age of 44.5. Hispanics were the youngest, with a median age of 30; and a quarter of all children in the U.S. were Hispanic. Black Americans who weren't Hispanic had a median age of 35.5. The number was for 37.2 for Asians.

Utah, home to the largest Mormon population in the U.S., was the youngest state, with a median age of 31.3, a function of having one of the nation's highest birthrates. The District of Columbia's median age of 33.9 was a close second because of the large number of young, working-age adults commonly found in urban areas. North Dakota was the only state where the median age declined, from 37 to 35.8, as an influx of young workers arrived to work in a booming energy sector.

Maine was the oldest state in the U.S., with a median age of 45.1, as more baby boomers aged out of the workforce.

Sumter County, Florida, home of the booming retirement community The Villages, had the highest median age among U.S. counties, at 68.5; while Utah County, home to Provo, Utah, and Brigham Young University, had the lowest at 25.9.

As one of the youngest baby boomers, Chris Stanley, 59, already lives in The Villages. She said her mission in later life is to let younger generations know they can change things despite perhaps not having the same economic opportunities she did.

"I want to impart the urgency that I feel," she said. "They can make it better."

While people 65 and older made up 16.8% of the 331 million residents in the U.S. in 2020, the share was still significantly lower than it was in countries such as Japan, Italy and Greece, where the age cohort makes up between more than a fifth and more than a quarter of the population. However, their share of the U.S. population will continue to grow as baby boomers age.

"In the long run, immigration is the only way the United States is going to avoid population decline," Cohen said.

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Follow Mike Schneider on Twitter at @MikeSchneiderAP