(The Hill) – Americans aren’t marrying young anymore.

The share of U.S. adults who are married by age 21 sank from about one-third in 1980 to 6 percent in 2021, Pew Research reports. The share who tie the knot by 25 plunged from nearly two-thirds to 22 percent.

Young adults have come to view marriage as a capstone event: Couples used to marry and build a life together. Now, they build the life first.

“There’s a longer checklist of items you need to complete before you’re considered marriageable,” said Susan Brown, professor of sociology and director of the Center for Family and Demographic Research at Bowling Green State University.

“You need to get a quote-unquote real job. You need to be living independently,” she said. “All of these milestones take time to achieve, and as we all know, many people aren’t ever going to achieve them.”

Young marrieds are a vanishing breed. In 1980, the average American male married at 25, the average woman at 22, U.S. Census data show. Today, the average first-time groom is 30, the bride 28.

Over recent decades, family researchers have tracked the rise of “unpartnered” Americans. In the prime adult years, ages 25 to 54, the share of married Americans has dwindled from more than two-thirds in 1990 to barely half today. Roughly one adult in 10 cohabits with a partner. Everyone else, in romantic terms, lives alone.

And the rising marriage age is only the most dramatic among several demographic trends that signal a postponement of American adulthood.

Late teens and twenty-somethings have “created this new stage between adolescence and young adulthood,” said Jeffrey Arnett, a psychology professor at Clark University. Arnett is credited with coining the term for a new life stage, emerging adulthood.

The share of American adults with full-time jobs at age 21 dwindled from 64 percent in 1980 to 39 percent in 2021. Many fewer young adults are living apart from their parents. In four decades, the share of 25-year-olds with children has dropped from 39 percent to 17 percent.

Young adults are staying in school longer. The share of Americans with bachelor’s degrees has nearly doubled since 1980, from 23 percent to 40 percent.

“The timetable of young adulthood has been pushed forward, and the single transitional event that has been pushed forward the most is marriage,” said Laurence Steinberg, a professor of psychology and neuroscience at Temple University and author of the new book You and Your Adult Child.

Like so much of young adulthood, the trend away from early marriage has a great deal to do with sex.

Not so long ago, sex outside of marriage was taboo in American culture. That stigma gradually faded, along with slackening societal prohibitions against living “in sin,” and even having a child, out of wedlock.

“The stigma associated with nonmarital childbearing has declined,” said Christine Percheski, a sociologist at Northwestern University. “That used to be a nontrivial part of the story about early marriage.”

As recently as 1960, the average American woman married at 20. The arrival of modern birth control in the 1950s and 1960s, and the advent of a constitutional right to abortion in 1973, which was rescinded last year, allowed millions of couples to delay the decision to wed, feeding the gradual rise in marriage age.

“It used to be, you dated, then you got married,” Brown said. “Then it was, you dated, then you lived together, then you got married.” That impulse gradually gave way to a growing consensus that “you can enjoy many of the benefits of marriage without being married.”

Indeed, American women are now having children at a younger age, on average, than getting married. Since the early 1990s, women are entering marriage later than motherhood.

Today, with fewer Americans feeling compelled to marry young, couples are reimagining marriage as a final rite of passage to adulthood.

That is not to say they have soured on marriage: quite the contrary.

“They idealize it as much as ever, maybe more than ever,” Arnett said.

Decades ago, many couples married out of economic expedience or perceived necessity. Now, young Americans don’t plan to marry until they meet their soulmate.

Roughly 80 percent of Americans still marry by age 40. That number has slipped over the years. But add in the nearly 10 percent of adults who are cohabiting, and the rate of “partnering” is close to 90 percent, Arnett said.

“Teenagers and young adults do aspire to get married,” Percheski said. “They just aren’t marrying as young as they used to, and they think it’s important to attain financial independence and complete their education first.”

Forty or 50 years ago, most Americans completed their education well short of a college degree and financial independence meant one good job, generally for the husband-to-be.

Today, as a prerequisite for marriage, “a lot of the research would suggest that couples want both people to have a good, solid job,” Percheski said.

By long tradition, marriage marks the first time many Americans settle into their own homes. That transition, too, is coming later.

The share of adults ages 25 to 34 who lived with their parents reached a historic high in 2020.

In the 18-to-29 demographic, the share of young adults living with their parents soared from 32 percent in 1980 to 52 percent in 2020, Pew data show. That figure retreated after the peak of the COVID-19 pandemic, but not by much.

“People are being forced into living arrangements that aren’t conducive to being married,” Steinberg said. “And if you can’t afford to move out on your own, what are your options? It might be delaying getting married.”

Young Americans with college degrees used to marry at lower rates than those without, a phenomenon researchers termed the college marriage gap. In recent years, it has reversed.

Today, young Americans with less education and income marry at lower rates than people with more education and money.

Between 1990 and 2015, Pew found, the share of adult Americans holding both a bachelor’s degree and a marriage certificate dwindled slightly, from 69 percent to 65 percent. But among adults with only a high school education, the marriage rate fell from 63 percent to 50 percent.

“There are huge social class differences in rates of marriage in this country, which have emerged in the last couple of decades,” Steinberg said.

“If you look at the top two quintiles by income,” the top 40 percent of American earners, “the rate of young people who are married in that group is the same as it was about 40 years ago,” he said. “It’s working-class and poor people who aren’t getting married.”

Marriage rates run lower, and divorce rates higher, among adults with less education and income. Money, or the lack of it, figures prominently in both trendlines.

Some researchers predict the nation’s average marriage age will continue to rise, along with other milestones of adulthood. In parts of Scandinavia, Arnett said, the median age of first marriage has reached 35. But he thinks marriage itself will endure.

“Marriage is a really durable institution,” he said. “It’s a rare human universal. It exists in all societies. So I don’t think it’s going anywhere.”