The American millennial generation is sneaking up on 40. The kids aren’t kids anymore.

But lots of them have put their lives on hold as if they’re still teenagers, fresh from school.

Is this a new lost generation?

For the first time in 130 years, there are more young adults 18 to 34 — 32.1 percent — living at home with mom and dad than in any other living situation, according to the Pew Research Center.

In addition to so many apparent failures to launch, many millennials aren’t having babies or getting married. They’re not buying houses.

They’re not sticking with jobs. A new Deloitte survey indicates that 43 percent of millennials expect to leave their current employment within two years.

You can blame it on their parents, if you’re so inclined. As a rule, they went along with the drive-up-the-self-esteem, everybody-gets-a-trophy way of raising children that started in the 1980s. Maybe that weakened a significant segment of an entire generation.

Maybe not. You’d be inferring that America’s most educated generation never caught on to the difference between winning and losing.

This generation, if lost, is lost for good reasons. The rug has been pulled out from beneath them, and these youngish people know it better than anyone. That includes the previous generation, which, consciously or not, did the pulling.

Some millennials are making good money, but they’re spending better money. The cost of housing, for instance, is probably higher than it’s ever been. It’s about 52 percent more now that it was at the turn of the century.

Millennials are wary of buying this expensive real estate because they have already mortgaged themselves to pay for their educations. The average college loan costs about $100 per week.

I’m a generation older, and I never had any college debt because my tuition cost $270 per year.

So modern college graduates have assumed substantial and often crippling debt for what their parents received, basically, for free.

It’s not just housing and education. The Economist Magazine’s “Big Mac Index” indicates the average cost of that harbinger hamburger has risen from $3.57 to $5.51 in 10 years. That’s a 54 percent increase during a period when wage growth totaled about 7 percent. So if the price of hamburgers is any indication, millennials, in the first of their peak earning years, are struggling to save or invest anything at all.

Whatever the pay, employers, as a rule, aren’t loyal to employees — young or old — and will lay them off at the drop of a hat. Some millennials return the favor. They apply for new jobs, and get them, but not necessarily show up when they do, becoming “ghost employees.” It’s a sort of network of mutual labor irresponsibility.

I think some of the ghost employees know they need to look for employers who care more about them, but they freeze, frightened of jumping from the frying pan to the fire.

A friend of mine who’s just over 30 asked me, “If I make $40,000 and she makes $30,000, do we have enough for children? Children are expensive.”

At first, I thought, of course, it’s enough. Then I realized that I was assuming that as his children get older, he and his wife would see their salaries increase. But that’s not at all guaranteed.

One of the causes of the 2008 economic crash was that some families who initially had enough income to pay their mortgages found, as time passed, that their pay stagnated, and they were barely able to cover. Then, if they had any medium-sized setback, they were stuck.

And soon, of course, as the economic downturn cascaded, many of them lost employment altogether.

This scenario is not lost on the millennials. It was playing out when they first started to consider saving for house down payments. They were watching when home values cratered, for the first time in decades, and they were watching when they became overpriced a few years later.

Millennials are unemployed twice as often as the rest of the workforce. They make about 20 percent less in real income than their parents did at the same age.

They are reasonably peeved by that, since they did what their baby-boomer parents told them, and went to college. Over 50 percent more young Americans have degrees now than in 1990, according to the Brookings Institution.

When many more kids go to college and many fewer into the trades — and that’s what’s occurred after most high school shop classes in the U.S. closed — there’s more competition for jobs that require college. That means millennials constantly hear the footsteps of younger, hungry contenders for their paychecks.

Another result of so many educated people is that you have a lot more smart folks.

And they can see that the game is rigged.

They know that they’ve been eating a lot of food that is extraordinarily unhealthy, and is created and marketed not for nutrition but for corporate benefit. They have similar knowledge about fossil-fuel energy. Medicine. Publishing. Politics.

And at the same time that such knowledge has been acquired by them, the actual value of amassing knowledge has diminished.

The answers to everything seem obtainable from an electronic gadget in our pockets. Institutional knowledge is no longer as important as it was. Millennials watch older coworkers walked out with their desk stuff in boxes because of that, and they know they may be similarly vulnerable before long.

So they work like dogs. They feel pressed for time, and opt to save some by ordering dinner on their phones on the way home. They’ve cheated themselves out of cooking, one of the great pleasures in life.

They can safely phone in transit because many have opted for public transportation and ride-shares to save money and reduce the annoyance of buying, insuring and maintaining cars. Maybe they try to get a little extra work done on the way. Can’t waste a minute.

All this money and time pressure might be a reason that millennials famously are more interested in experience than material possessions. They travel more, for instance, and buy less. This travel takes place both during vacations and, increasingly, after quitting jobs.

Their wanderings are reminiscent of the Lost Generation of 100 years ago. That generation was first decimated by the loss of promising men in the trenches of World War I. Then, some of those who survived aimlessly traveled the planet, seeking experiences instead of moving their lives forward.

It’s not that bad, of course, for this lost generation. But as a result of all the pressure and all the attempts to escape from it, they are also missing some significant moments in life.

They may be able to tell their grandchildren about what it was like to see the Greek islands in 2012. But so far, it doesn’t look like they will be able to tell them what it was like to save the world for them.

About how they fought to end the war in Syria, stopped the Rohingya genocide, solved the South American refugee crisis.

How they pushed this country over the last hurdles to make it a leader in sustainable energy. Fought to educate the nation about the illnesses caused by processed food.

They don’t push for more public transportation. They just ride it.

They should be the core of a new political class, but they are sorely underrepresented compared to previous generations. They seem disillusioned by the system that got them where they are.

It’s relatively rare when a member of their age segment runs for anything. In their lifetimes, the average age of members of Congress has risen from 49 to 57.

This generation is not so much lost as Missing in Inaction.

If they’re planning on taking on the world’s problems later, after they’ve somehow achieved great success, they are probably kidding themselves. If that were possible, Bill Gates would have saved us all by now, right?

Millennials should consider rolling their sleeves up now, and working together, when they still have some youthful energy. Now, when some of the things that need changing are not too intractable.

They were born, mostly, of the generation that, when young, ended the Vietnam War. The Baby boomers eventually decided that they were too busy to fix all the broken things in the world. Now, their children are too busy, too.

They really are busy. It’s true.

But it’s also true that if you want something done, ask a busy person.

— Leavitt: Millennials — our own lost generation —-