“Whatever you imagine your life is going to be like, know your life is not going to be anything like that,” one character tells another in the picaresque comic drama “20th Century Women.” The voice of wisdom is Abbie (Greta Gerwig), a lodger in a shabby Southern California rooming house in the summer of 1979. Her young protege is 14-year-old Jamie (Lucas Jade Zumann), who lives there with his single mother, Dorothea (Annette Bening), the landlord. Abbie takes him to punk nightspots to experience the new wave vs. punk music scene, and she lends him her copies of “Our Bodies, Ourselves” and “The Second Sex.”

Dorothea wholly approves of Abbie’s tutelage. She’s the one who drafted Abbie to help her son come to terms with what awaits him. It isn’t what he expects, and that’s the point.

Whatever you imagine a family-focused movie is going to be, know that this is not going to be anything like that. Bringing up Jamie is one of the central concerns of Mike Mills’ episodic film. It’s set in a time when the 1950s vision of suburban normality was breaking down, innocence was not extinct, and long, deep conversations around dinner tables were the height of social networking. With the aid of Abbie and William (Billy Crudup), another renter and hippie handyman, Dorothea hopes to guide her perplexed son out of drifting confusion, help him cope with messy relationships and chart a path toward a workable adulthood.

With its theme of misunderstandings between a well-meaning parent and child, the film is a companion piece to Mills’ 2010 debut film, “Beginners.” There he drew from autobiographical material to examine issues between a newly open gay older man and his adult son in what seemed a forlorn “poor me” manner. This time Mills excavates his own life story again, creating a nostalgia piece about his relationship with his complicated mother.

There’s a feeling of self-involved back-patting in each film, but here a largely upbeat tone and sterling performances reduce that to a hairsplitting gripe.

The film’s greatest strength is its specific set of characters. While no big events or personal crises happen, no one seems two-dimensional or thin. Gerwig’s Abbie is an aspiring artist with a creative streak as vivid as her crimson-dyed hair. William is a mellow California dude, played by Crudup with more depth than you’d expect. Fanning tears ferociously into her role as a confused, sensitive heartbreaker, while Bening is as good as ever, scene by scene owning the movie in the role of a nurturing female who regards males like a benign but alien species.

In its way, with its focus on broken families, nervous but heroic young protagonists and a plot about home, believing and trusting, this feels like a ’70s Steven Spielberg movie, minus the special effects. It’s not exclusively about the kids near the center, and definitely not a kids’ film. It warns us no matter what age we are, we’re still in middle school.

MOVIE REVIEW

“20th Century Women”

Grade: B

Starring Annette Bening, Greta Gerwig and Lucas Jad Zumann. Directed by Mike Mills.

Rated R for sexual material, language, some nudity and brief drug use. Check listings for theaters. 1 hour, 58 minutes.

Bottom line: A nostalgic piece about a relationship with a complicated mother