Job seekers meet with recruiters during the Quad Cities career fair in Moline, Ill., earlier this month. Photographer: Daniel Acker/Bloomberg

It's something that's started to get on peoples' nerves in pop culture: Hollywood seems totally open to older male actors, but aside from the Helen Mirrens of the world, leading women seem to age out at about 30.

Well, it looks as if the same dynamic is at play in the broader working world, as well.

A new working paper out from the National Bureau of Economic Research, based on what is probably the largest field experiment to date testing the prevalence of age discrimination in hiring, shows that the résumés of older women get far fewer callbacks than those of older men and of younger applicants of either sex.

Independently, neither of those phenomena — age discrimination and sex discrimination — are really news. A number of studies over the years have demonstrated that for certain fields, women and older people will either be hired less frequently or paid less, or both.

But study authors David Neumark and Ian Burn of the University of California at Irvine and Patrick Button of Tulane University thought that the way in which hiring discrimination is usually detected — through dummy résumés sent out in response to real job postings — might have been flawed, because they test responses to older and younger applicants with "commensurate experience." Even a rational hiring manager might have doubts about a 50-year-old who has the same number and type of jobs on his or her résumé as a 25-year-old, after all.

Instead, the researchers set out to craft résumés that more realistically reflect experience that someone older than 45 might have, without making them clearly more qualified for the job. And it was a big endeavor. The researchers studied thousands of résumés to understand who applies for what and how they present themselves. They then designed fake documents in four job categories, three age brackets and a dozen cities. In all, more than 40,000 résumés went out in response to online job ads — many more than other recent studies on the subject.

The results were fairly clear. The study tested employment categories — administrative positions, sales associates, janitors and security guards — that might be both accessible to young people and desirable for older people transitioning from a career into less demanding employment.

Overall, fictional workers age 49 to 51 got 18 percent fewer callbacks than those age 29 to 31, and workers age 64 to 66 got 35 percent fewer callbacks, showing a strong bias against older applicants. But for administrative jobs, using a sample of only female applicants, those age 49 to 51 got 29 percent fewer callbacks than applicants age 29 to 31, and workers age 64 to 66 got 47 percent fewer callbacks. Sales jobs, which had applicants of both genders, also showed a much greater premium on youth for women than for men.

So what explains these differences? The researchers aren't sure, but they have some ideas.

"There are two related possibilities," the authors wrote. "One is that age discrimination laws do less to protect older women who may suffer from both age and sex discrimination." In other words, it's difficult to bring claims based on actions that violate the Civil Rights Act and the Age Discrimination in Employment Act. But that's not all.

"Second, older women may in fact experience more discrimination than older men, because physical appearance matters more for women and because age detracts more from physical appearance for women than for men," they write, citing sociology research from the past couple of decades that supports that hypothesis.

This isn't just of interest for academics. As people live longer, and the American public is less well protected in retirement by healthy pensions or employer-matched 401(k)s, creating opportunities for older people to support themselves if they're able could ease pressure on an already overburdened social safety net. Women live longer than men on average, meaning they could benefit even more from continued employment. Cutting them off simply because of their age could meaningfully affect their quality of life.

Of course, there are different arguments for giving younger people those opportunities instead — and they have already been used to justify employment programs targeted at "opportunity youth," or those who haven't gotten a chance to fill out that first line on their résumés.

Ultimately, that's why creating more jobs is probably the best thing that can be done to help. Everyone benefits when employers can't afford to discriminate based on anything other than someone's qualifications for a job.