Under normal circumstances, a girl named Banger would curse the one who named her. But for the women in “The Banger Sisters,” the title is an honor given to them — two dutiful young groupies — by the one and only Frank Zappa. You can figure out why.

Of course, you can’t be a groupie all your life. Or can you? Bob Dolman’s film offers a generic and somewhat careless examination of an alternate lifestyle, and how compatible it is with the process of growing old. Call it “Once Famous.” As a buddy picture, “The Banger Sisters” is enjoyable enough, benefiting from likeable actors playing quirky characters.

But the friendship between the “sisters,” actually former roommates, does little to answer the original and provocative questions about aging and transforming. An excessive amount of screen time is spent bringing Lavinia (Susan Sarandon) and Suzette (Goldie Hawn) together, and having them reminisce and reconnect. Dolman dotes on the nostalgia of girlhood far too much, and not sufficiently on the beauty of womanhood, a quality that Lavinia and Suzette only vaguely grasp at the end of the picture.

The film’s opening sequence does well to establish Suzette’s feelings of inadequacy regarding the process of growing old. She’s a bartender at the hip Whiskey A-Go-Go in Los Angeles, where the young and angry members of a punk band scream before a writhing crowd of scantily clad young women. When Suzette’s boss is about to fire her, she offers in her defense, “I’m fun, people love me. I’m Suzette!” Only someone with Hawn’s charm can pull off this bubbliness without being too saccharine. Later the same night, she tries to relive the good old days by hitting on the lead singer, before realizing that he’s busy with a teenage groupie.

After returning to her opium den of an apartment and flipping through old photographs of the days when her mojo was still rising, Suzette decides its time to really rekindle her past — and bum some money — by finding her old partner in crime, Lavinia. She sets off for Phoenix, picking up the disenchanted screenwriter Harry Plummer, played by Geoffrey Rush, after he agrees to buy her a tank of gas.

Hawn and Rush are an amusing pair, but there isn’t much chemistry between them — though we’re meant to believe so later in the film. Nonetheless the juxtaposition of two such opposite personalities is always fun to watch, particularly when the roles are played by good actors. Rush’s voice is so nasal that anything he says sounds like a complaint, and it works. Hawn is funny and poignant in a way we haven’t seen since “The First Wives Club.”

After checking into a hotel with Harry, Suzette eventually works up the nerve to speak to her old friend, who doesn’t recognize her. Even when she eventually does recognize her, she offers her $5,000 to leave and never come back. Lavinia has locked the door on her past, content to live the wealthy suburban soccer-mom lifestyle. But after a few hours with Suzette, Lavinia falls into the depths of a midlife crisis, chopping off her hair and whipping out the snakeskin pants.

Pretty soon it’s just like old times: The girls smoke a 20-year-old blunt while looking at their “Rock Cocks,” a set of celebrity penis Polaroids. In one really hilarious scene, Lavinia laughingly attempts to explain to her husband that some people collect baseball cards, and others collect Rock Cocks.

Up to this point “The Banger Sisters” amuses with its many clashes of personality types, most of which occur in places prone to awkward situations (bathrooms, family dinners, hot-boxed basements). When Lavinia is no longer the voice of conservatism for Suzette, Lavinia’s family takes over, expressing outrage at her sordid past.

Lavinia’s teenage girls, played by Erika Christensen (in a step up from “Swimfan”) and Eva Amurri are justifiably self-righteous about the whole affair. Her husband, a strait-laced lawyer and wannabe politician, does his best to play along with Lavinia’s nostalgia (well, at least until he sees the Rock Cocks).

The friendship between Lavinia and Suzette is a strong but trivial one. It should have matured over the years but then again, we never learn why the two grew apart in the first place.

Dolman wants us to believe the women are bonding as they never have before — he even cues the cheesy music — but nothing suggests growth or transformation. Sadly, too little is known about their relationship during their groupie days, so the characters don’t seem complete. There are no flashbacks of any kind; instead, there is only the unceasingly pleasant haze of nostalgia.

The ending of “The Banger Sisters” is one of hasty resolutions. Lavinia’s family suddenly falls into place, accepting her past and her personality. Suzette seems a bit more mature. But the transformations in the characters are trivial and formulaic. Similarly, the friendship remains static. “The Banger Sisters” has its humor and talent, but it fails to show progress in its characters. Worse, it refuses to answer the questions about age that the plot raises, instead letting them linger uncomfortably in the background.