It takes an incredible performance to stand out in the terrific cast of Mike Mills’ “20th Century Women,” but Annette Bening is that good as Dorothea, a single older mom raising her teenage son, Jamie, in California in 1979. Like Mills’ other, wonderful film “Beginners” (2011), this film is autobiographical, and surely that helps give the characters their incredibly watchable, endlessly fascinating feel of authenticity.

As the title suggests, many of the characters are, in fact, women. Dorothea rents a room in their large, dilapidated house to Abbie (Greta Gerwig), a confident but damaged photographer recovering from the aftermath of cervical cancer. Elle Fanning plays Julie, the unhappy best friend to protagonist Jamie, who is suffering unrequited love for the girl whose home life is so unhappy she sleeps over, in a sisterly fashion, every night.

Jamie and Dorothea both revel and wallow in their open-house lifestyle, and when Dorothea begins to fear for her son’s mono-parental upbringing, she enlists the help of the aforementioned females to add their perspective. This casual plan is the closest the film comes to a plot, and is really just an excuse for a series of perceptive, well-written anecdotal scenes.

Abbie takes Jamie to a punk club and gives him tips on dancing and picking up girls; Julie tries to teach him how to look confident smoking. These can’t have been exactly what Dorothea had in mind, but what makes her so wonderful is that she isn’t overly upset about it either. Bening exudes curiosity and intelligence, and is open to most experiences for herself and her son, yet their extra-wide generation gap always adds a layer of complexity to their relationship.

It’s interesting Dorothea feels it is her age, but not her gender, limiting her parenting point of view. One of her boarders is male, yet she asks the women to pitch in with Jamie. The guy is the truly wonderful Billy Crudup, who looks more at home in the 1970s, in this and most films, than he does in his own time. He’s a sweet, helpful hippie, casually espousing meditation and other practices from his commune days. He’s a gentle love interest to various characters, and fully realized despite his relatively short screen time.

This is a novelistic movie in its structure, as characters reach into their pasts and even describe their futures, stretching the film’s perfectly rendered moments in both directions. Since “20th Century Women” is based in the writer-director’s own life, this makes sense; he knows the entire story.

The film’s characters are richly drawn and beautifully portrayed. They are individuals, and the small moments depicted here illume the lives we’re told they will have in the future. Mike Mills places his characters meaningfully in a larger historic context, given the benefit of hindsight, and there are moments that echo the times we are in now.

A group gathers around the TV watching Jimmy Carter giving his plaintively emotional “crisis of confidence” speech about the hollow heart of consumerism, and the resonance for modern viewers has probably grown with each day. From the pivotal pre-Reagan moment in history, to the deeply personal moments in the filmmaker’s’ own remembered youth, “20th Century Women” will leave you feeling as though you were there, too.

“20th Century Women” is currently available to rent.