It doesn’t limit “20th Century Women” to call it a “coming of age” story.

Because there is no limit to that which comes of age in it.

Sure, there’s a teenage boy, Jamie (Lucas Jade Zumann). And he’s got this crush on a bad girl/broken spirit, Julie (Elle Fanning) who keeps coming over, leaning on him, spending the night and insisting that unlike every other guy she knows — she’s promiscuous — with Jamie she’ll “just be friends.”

His Santa Barbara, California mom (Annette Bening) “had me at 40” and is raising him by herself, something fairly novel even in California in 1979.

She studies him, frets over giving him a complete and well-rounded upbringing. But you kind of figure she’s coming of age, too, in between her pearls of tough-love wisdom.

Mother and son are brutally blunt with each other in that hip, sitcommie post “One Day at a Time” way of the late ’70s.

“Having your heart broken is a tremendous way to learn about the world!”

There’s a fragile, winsome boarder (Greta Gerwig) and free-spirit handyman (Billy Crudup) also under their roof.

And in 1979, America was coming of age — again — about to abandon the serious search for answers to the future and retreat into a deluded nostalgia that lasted for a decade.

So maybe writer-director Mike Mills (“Beginners”) was onto something, tapping into an exhausted zeigeist that suggests America, like Dorothea, Bening’s single-mom in the movie, is earnest and overwhelmed and maybe too tired to get everything just right, to always do right by everybody. She’s not going to be everyone’s friend, not going to get the answers from assorted feminist studies texts.

But being an adult and a mom, she can’t just check out. So the decisive, authoritative Dorothea gets on with it, prioritizing who she wants Jamie to become, enlisting Abbie (Gerwig) and then Julie in her mission. He’s got to be a man who’s a comfort to women, treat them honorably no matter what.

Over the course of the film, his mother and the other women in his life test Jamie, teach him, and on purpose or utterly by accident make him the man he will become.

It’s a sweet, sad-faced comedy in a minor key, with Bening holding forth as the iconic woman of the “20th Century” of the title. Dorothea is unflappable long before she needs to be. This may be mid “malaise” America. But she is pre-Reagan, pre-AIDS, pre-REAL recession.

Gerwig plays a more brittle version of her usual screen flakes, Crudup is perfectly cast as that rooster in the henhouse just outgrowing his “hippie” phase. Young Zumann holds our interest well enough for us to want to follow his story even though we know every other character in this has a more interesting one.

And Fanning, a wise-beyond-her-years starlet, is right on the money as a lost girl in ’70s straightened hair, catnip to the boys not just because of her looks, but thanks to the air of doom that hangs over her.

It’s not a deep film, but it is a rich one — full of flesh and blood characters, realistic “coming of age” moments and pithy homilies on the state of relationships, gender roles, “the California Dream” and the American one.

And as its title suggests, it’s a real showcase for three generations of the best American actresses in the business, women of feelings and heart and steel. They give Mills’ movie its backbone and in the malaise in which this film reaches us, a hint of hope.

MPAA Rating: R for sexual material, language, some nudity and brief drug use

Cast: Annette Bening, Greta Gerwig, Lucas Jade Zumann, Elle Fanning, Billy Crudup

Credits: Written and directed by Mike Mills. An A24 release.

Running time: 1:59