Hillary Clinton speaks during a fundraiser at the Capitol Hill. She’s 68, and younger than Donald Trump. (Brendan Smialowski/AFP/Getty Images)

A woman her age is supposed to be invisible. But Hillary Clinton, who is 68, refuses to disappear — and there is no shortage of people who despise her for it.

One voter at a Donald Trump rally described her to The Washington Post’s Jenna Johnson last week as “an angry, crotchety old hag.” Trump, who isn’t exactly a spring chicken at age 70, claims Clinton lacks “stamina” and a “presidential look” and mocked her by acting out her stumble when she had pneumonia last month.

There’s misogyny, and then there’s the ageist misogyny that older women face. That under­current runs very deep in our culture, and it’s one of the reasons the haters hate Hillary Clinton so deeply.

No one has talked about this much, but it’s a very real phenomenon in this election.

The presidential nominee is confounding America because she represents a demographic that our culture secretly dislikes: older women.

At a rally in Manheim, Pa., Oct. 1, Republican presidential nominee Donald Trump mocked Democratic rival Hillary Clinton stumbling during a 9/11 ceremony after she had been diagnosed with pneumonia. "She's supposed to fight all these different things, and she can't make it 15 feet to her car," Trump said. (The Washington Post)

Everyone is guilty — even women themselves. Earlier polls showed that women Clinton’s age supported her, but younger women overwhelmingly supported Sen. Bernie Sanders.

Maybe a wise grandpa made sense to them. But grandma? In the Oval Office? Shaking their heads. Does. Not. Compute.

America worships youthful femininity, and our pop culture, if not our policies, idolizes mom. But what do we do with women once they’re not in either of those roles?

[She ditched her $400,000-a-year legal job after her ‘woman’s card only held her back]

We minimize and ignore them.

The older, wise woman has rarely had a starring role in the American story, beyond grandma and her cookies.

Plenty has been said about the way American women feel invisible once they reach 60, or 50, or — gack — even 40 today. We live in a culture where gorgeous Maggie Gyllenhaal is being told she’s invisible before she’s out of her 30s.

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“I’m 37, and I was told recently I was too old to play the lover of a man who was 55,” Gyllenhaal told the Wrap last year. “It was astonishing to me. It made me feel bad, and then it made me feel angry, and then it made me laugh.”

Most women in this age bracket remember the day they realized they had become invisible — that moment when the salesman pushing a big-ticket product looked right past them (even though they were the only person in his periphery who could actually afford the thing), when the clerk who was so chatty with the guy in front of them ignores them, when the intern treats them like a nonentity rather than an experienced superior.

This isn’t only about the silencing of catcalls and other changes that come with age. Most women welcome the end of that attention. No, there’s something deeper and more inhumane about the dismissal.

There are plenty of countries for old men in Hollywood, though, according to a study on diversity in the entertainment industry released earlier this year by the University of Southern California’s Annenberg School for Communication and Journalism.

The study looked at 414 scripted movies, TV shows and digital series from major media companies that aired for 12 months between 2014 and 2015. Of the characters older than 40? Men got 80 percent of the roles.

Hello, Hollywood. There are older women besides Helen Mirren, Judi Dench and Meryl Streep.

The situation is not too different for women at less glamorous workplaces.

Another study — this one done last year by economists at the University of California at Irvine and Tulane University — looked at what happened when 40,000 fake résumés carefully created to reflect a breadth of age-appropriate experience were sent out for all kinds of jobs in cities across the country.

And, yup, you guessed it. The number of callbacks for older women was way lower than for younger women. In some cases — administrative jobs — 47 percent lower. But when it came to men, young and old got equal shots at jobs, wrinkles and ear hair be darned.

Corporate America is the axis of evil when it comes to the sexism/ageism intersection.

The tiny minority of respected, older women — just 4 percent of American Fortune 500 companies have female CEOs — have persisted and struggled and fought to earn positions of power that are usually an inevitable evolution for men of their skill and experience. They get talked over in meetings, interrupted and passed over for promotions, while usually being criticized for their ambition. Indra K. Nooyi, the 60-year-old chief executive of PepsiCo, said she had to work twice as hard as the men around her.

Powerful older women? We apparently still can’t get our heads around this concept.

Some of this is because women simply didn’t have the opportunity to get into the white- collar workforce in a meaningful way until the 1970s. Congress is still only 19 percent female. Heck, we’re not even 100 years into women being able to vote.

[Born before women could vote, these 100-year-olds want Hillary to make history]

So it’s taking a while to accept that women can be maidens, mothers and, yes, leaders, too.

What about all that wisdom, experience, the things they’ve seen, the things they know?

Discarding older women means discarding years of knowledge and know-how.

The “grandmother hypothesis” even suggests that older women — and killer whales, the only other species to go through menopause — are biologically made to lead. That’s why their fertility ends, so they can get to the business of being leaders to all those creatures they created.

But there is hope that the invisibility trend is fading.

At 83, Supreme Court Justice Ruth Bader Ginsburg is so respected, she’s got a street name: the Notorious R.B.G.

Earlier this year, Ginsburg caused a furor by declaring Trump a “faker” and worrying about the impact on the country if he won the election. The Republican candidate quickly dismissed her, claiming her “mind is shot.” Not really, Donald. It’s pretty clear that Ginsburg is sharp, brilliant and relentless. And she has also made it clear that she’s not going away anytime soon.

Alongside her are Massachusetts Sen. Elizabeth Warren, 67; Federal Reserve Chairwoman Janet L. Yellen, 70; and International Monetary Fund Chief Christine Lagarde, 60.

It’s time to get used to it. Older women will be invisible no more.