The title of Mike Mills’ autobiographical film about a teenage boy raised by a single mother, “20th Century Women,” is wonderfully evocative. Without yet knowing anything else about it, we’re thinking about what it means to be modern and female — which of course also makes us wonder about what it means to be male. The words that appear on the screen when this movie begins speak just as loudly: “Santa Barbara, 1979.”

It’s the perfect time and place for a story of adolescent confusion. Lucas Jade Zumann plays Jamie — Mills’ alter-ego — a sensitive boy growing up in a world where old rules no longer apply but new ones have yet to be set, if ever. His mother, Dorothea (Annette Bening), is an eccentric divorcee who rents out rooms in their house, and although one is occupied by a graying hippie, William (Billy Crudup), there’s no proverbial male role model for Jamie. So Dorothea takes a different tack, enlisting help from her other lodger, a punk-rock photographer named Abbie (Greta Gerwig), and a sexually precocious neighborhood girl, Julie (Elle Fanning). Maybe three women, mom seems to reason, can turn Jamie into a good man.

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As you might guess, Jamie is in for a rocky ride. Abbie introduces him to great bands — The Raincoats, Talking Heads — and teaches him how to throw off a too-cool masculinity, but she also feeds him a diet of furious feminist literature. Julie, meanwhile, engages in casual sex with local layabouts but uses Jamie as her teddy-bear, sneaking into his room at night for a celibate snuggle. William grooves along in the background, a well-grounded guy that nobody seems to take seriously.

“20th Century Women” is filled with terrific performances, particularly from Bening as the deeply flawed Dorothea. Still, the movie has an odd way of avoiding emotional catharsis. Jamie never explodes the way we wish he would, which leaves us wondering what conclusions Mills has come to about his weird, wild childhood. In an odd way, this movie’s main weakness is also one of its strengths: it raises more issues than it can fully explore.