Noah Smith is a Bloomberg Opinion columnist. He was an assistant professor of finance at Stony Brook University, and he blogs at Noahpinion. Read more opinion LISTEN TO ARTICLE 4:15 SHARE THIS ARTICLE Share Tweet Post Email

Photographer: T.J. Kirkpatrick/Bloomberg Photographer: T.J. Kirkpatrick/Bloomberg

The great irony of the ironic "Ok boomer" trope being enthusiastically used by millennials is that they themselves are the older generation to which the term increasingly applies.

The millennial generation -- generally defined as those born in the 1980s and the first half of the 1990s -- is approaching middle age. In less than two months, the oldest of this group will turn 40. The generation so recently depicted as rebellious youth intent on reshaping American culture will become eligible for protection under the Age Discrimination in Employment Act. The youngest millennials will be 23, meaning that college campuses will be almost entirely ceded to the next population cohort, Generation Z.

But millennials, whose numbers surpass those of the baby boom, don’t have many of the trappings of a generation approaching middle age. As economist Gray Kimbrough has documented, a large number of people in their 20s and early 30s live with their parents, while correspondingly fewer own their own homes. They’re also significantly less likely to be married than past generations:

Single, Not Necessarily Loving It Marriage rates by generation Source: Pew Research Center

These trends are among the reasons millennials are having fewer children. And those who do are having them later.

Why have so many millennials experienced failure to launch? Part of it might simply be the result of changing culture; dating apps and a liberalization of sexual mores, as well as the rise of roommate living, may have made some millennials reluctant to give up the urban bohemian lifestyle. But this probably isn't a major reason. Surveys show that the average number of children women want has remained steady at about 2.5 since 1970 and may have even risen slightly. Meanwhile, the decline in marriage is much more pronounced among less educated and lower-income Americans.

Instead of culture, millennials’ lifestyles are best explained by education and economics.

In the days of unions and manufacturing it was often possible to get a good middle-class job with only a high school degree. Those days are long gone. Since the early 1970s, weekly earnings for men without a college degree have declined while those for women have barely budged. The only men with rising earnings are those with post-college education. That implies that even a bachelor’s degree is no longer enough to reach the middle class. Professional degrees, master’s degrees and various forms of postgraduate certification are becoming the norm.

The rising importance of higher education means that a young person who could start a career at 22 or even 18 a few decades ago now has to wait until their late 20s or even later. That means that even educated millennials begin saving money much later in life, delaying the day when they’ll be able to buy a house.

It also may mean they earn less money over the course of their careers. Traditionally, earnings tend to plateau when people reach their mid- to late-30s. As education increases, this plateau might be pushed forward a bit, but research shows that older workers simply tend to be less productive on average; more education means a shorter window of prime working years and a shorter window in which to accumulate the wealth necessary to raise kids.

On top of that, millennials have had to fight against strong economic headwinds. A substantial percentage graduated during the Great Recession of 2008-9 or the years of slow growth that followed. Studies show that graduating into a recession reduces lifetime earnings. The housing bubble, meanwhile, dealt an unprecedented blow to the wealth of those in the middle of the distribution and lower:

Hurt More at the Bottom, Recovered Less Change in index of household wealth* Source: Federal Reserve Bank of Minneapolis

And on top of all that, inequality has risen substantially. Although educated millennials must delay saving for houses and kids, their less-educated peers are often never even able to start.

So for many aging millennials, the lifestyle of extended adolescence -- living with parents or roommates, finding dates on Tinder, starting relationships and breaking up again -- is probably beginning to seem less like a never-ending party than a trap. Even modern workout regimens and diets can’t eternally postpone the day when skin begins to sag, joints begin to creak and mental acuity begins to dull.

Maybe it’s no great surprise, therefore, that millennials are turning to socialism, clamoring for student-debt forgiveness and embracing presidential candidates who promise bold schemes of wealth redistribution. So this generation should be thought of not as youthful rebels infused with the vigor of naive idealism, but as embittered adults heading toward middle age before their finances are in order. More to the point, millennials are a lot like boomers who just never got a chance to boom.

This column does not necessarily reflect the opinion of the editorial board or Bloomberg LP and its owners.