To cite a generational icon - and there's a lot of that going on in While We're Young - I believe it was Mr. Wizard who used to proclaim, "Be just what you is, not what you is not. Folks what do this has the happiest lot."

OK, maybe that dates me (but hey, King Leonardo cartoons were in reruns for decades). Still, if there's a moral in Noah Baumbach's cuttingly comic and keenly observed new film, surely it's that same message Mr. Wizard gave to Tooter Turtle every time the hapless reptile returned from his latest wish-fulfillment disaster.

Ben Stiller, who starred as an alternate Baumbach in the writer/director's 2010 dark comedy, Greenberg, is back in similarly self-doubting and disdainful mode in While We're Young. He's Josh Srebnick, a New York documentarian who's married to Cornelia (Naomi Watts), also a filmmaker - and the daughter of a really famous one (Charles Grodin). The couple are in their mid-40s, childless, and mostly glad about that. Josh has been taking years to finish his opus, an investigation into "how power works in America," that he hasn't been able to pare down from 61/2 hours. In search of guidance, he reluctantly shows the rough cut to his father-in-law. Dad tells Josh that it feels like seven.

All that psychological constipation is relieved - with increasing exhilaration - when a twentysomething duo played by Adam Driver and Amanda Seyfried enter the picture. He's Jamie, a fledgling filmmaker who professes his awe and admiration for Josh's early, little-seen work. She's Darby. She makes ice cream. They share a loft with a lithe roommate who walks around without clothes. There's wall-to-wall shelves of vintage vinyl, and Jamie actually bangs his scripts out on a typewriter. How cool is that?

Very cool, in Josh's eyes. As he, and then Cornelia, become smitten with Jamie and Darby, the older pair find themselves going to dance clubs and sidewalk cookouts with their new young friends. Josh retrieves the wing tips he used to wear, finds a hipster chapeau just like Jamie's, and accompanies his buddy around town on a bike. Cornelia goes with Darby to hip-hop exercise class. Then the foursome spend an immersive weekend at an "Ayahuasca ceremony" where a shaman directs everyone to ingest a sludgy psychedelic so they can "vomit up their demons."

How cool is that?

Things get less cool for Josh and Cornelia when While We're Young follows the quartet on a filmmaking expedition upstate. Josh starts questioning his own motives, and Jamie's, too. The friends that Josh and Cornelia used to see socially - played with shocking grown-up-ness by Adam Horovitz, a.k.a. Ad-Rock of the Beastie Boys, and Maria Dizzia - don't know what to make of their pals. First Josh and Cornelia didn't want kids, now they're hanging with them.

Baumbach, whose films include the searingly funny, autobiographical The Squid and the Whale and the brilliantly uncomfortable Margot at the Wedding, writes wry, sharp, poignant stuff. His actors inhale and exhale their lines with utter conviction, and Stiller and Watts radiate the rumpled familiarity of a long-married couple with ease. (Watch the way they unthinkingly maneuver around each other in the bathroom.) But two-thirds of the way in, as plot twists rise to the surface and tensions mount, While We're Young loses some of its edge, its focus, and maybe its point, too.

That's not to say the adventures of Josh and Cornelia aren't worth watching. They are, indeed. "What is the opposite of 'the world is your oyster?' " he asks her at a particularly dire turn.

Mr. Wizard, for one, could provide an answer.

While We're Young *** (Out of four stars)

Directed by Noah Baumbach. With Ben Stiller, Naomi Watts, Adam Driver, Amanda Seyfried, Adam Horovitz, Charles Grodin. Distributed by A24.

Running time: 1 hour, 37 mins.

Parent's guide: R (profanity, nudity, drugs, adult themes).

Playing at: Area theaters.EndText

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@Steven_Rea