Writer and director Noah Baumbach’s latest movie, “While We’re Young,” follows a 20-year theme in his work into middle age. (Matt McClain/The Washington Post)

Twin themes — the struggle to grow up and its converse, the reluctance to do so — lie at the heart of Noah Baumbach’s work. It’s a leitmotif that first manifested itself two decades ago, with the then-26-year-old filmmaker’s debut, “Kicking and Screaming” (1995), a smarty-pants look at a group of post-college pals who can’t seem to get out of first gear.

Baumbach describes his artistic vision as a kind of hindsight. “I remember talking to a friend of mine, and we were referring to a past experience we both had. He said suddenly, ‘Well, I was so depressed then.’ I remember thinking, ‘You never talked about it then.’ It was something that he was only now coming to terms with.” All of his work, the filmmaker says, is an effort to dramatize the “drip-drip” nature of experience, in which breakthroughs come slowly and are often late, if they arrive at all.

Never has the elusive nature of maturity seemed quite so slippery as in Baumbach’s latest movie, “While We’re Young.” Considering that its stars (Ben Stiller, 49, and Naomi Watts, 46) are no spring chickens, the film’s very title offers a sardonic commentary on the march of time and those who choose to keep time to the beat of a different drum.

The film centers on New Yorkers Josh and Cornelia, a married couple in their 40s who are in a state of denial about encroaching middle age. When they meet Jamie and Darby, millennial hipsters played by Adam Driver and Amanda Seyfried, the intergenerational friendship briefly rejuvenates the older protagonists.

Baumbach’s dialogue is typically wry. “I remember when this song was just considered bad,” Josh tells Jamie, who’s listening to “Eye of the Tiger” on giant headphones and wearing a “kiss the chef” apron while barbecuing on a Brooklyn sidewalk.

Baumbach sat down recently for a wide-ranging chat that meandered from the philosophy of French director Jean Renoir’s “The Rules of the Game” (1939) to the emotional truth of the sitcom “Cheers.” (“Sam isn’t that stupid,” Baumbach recalls his father — writer and film critic Jonathan Baumbach — telling him.)

Sporting a mop of shaggy, jet-black hair, Baumbach doesn’t look that different, if you squint, from the enfant terrible who outrageously burst onto the indie-movie scene 20 years ago. Pairing purple New Balance sneakers with a stodgy sports coat, he exudes the mature yet laid-back air of a cool college professor — tenured, not adjunct — albeit one with some sort of Dorian Gray thing going on.

How is it possible that Baumbach, 45, is a grown man when he still looks like the whiz kid from “Kicking and Screaming”?

Baumbach, for his part, sees his overarching theme as something other than growing up. Rather, he says, his movies are “all about the psychology of relationships over time. All my movies deal with that to some degree: this notion of maintaining relationships through periods of change.”

According to Baumbach, “While We’re Young” stemmed from his desire to make a comedy about marriage — or more specifically, a “comedy of remarriage.” Popular in the ’30s and ’40s, the genre, a subset of screwball comedy, involves marriages on the rocks.

Baumbach, whose ex-wife, actress Jennifer Jason Leigh, filed for divorce in 2010 after five years of marriage and one son — named Rohmer, after the French director Eric Rohmer — is dating Greta Gerwig. The 31-year-old actress starred in Baumbach’s “Greenberg” (2010) and “Frances Ha” (2012) and has collaborated with Baumbach on several scripts, including “Frances” and the forthcoming “Mistress America.” Although the filmmaker has certainly turned to his own life for material before, Baumbach calls “While We’re Young” less autobiographical than generically personal.

“There’s nothing strictly true about this movie,” he says, describing his approach to storytelling as growing out of what he calls life’s universal questions: “How can you be the best version of yourself and maintain your responsibility to your own self and to your own growth, and how does that affect the people around you? Are you going on this thing together, or are you going to end up having to go in different directions?”

The mistakes Baumbach’s characters make render them, at times, unlovable. “Greenberg,” for example, was a tough sell, its focus on an abrasive curmudgeon — it was Stiller’s first film with Baumbach — who alienates almost everyone, except the character played by Gerwig. Nicole Kidman’s haughty and competitive star turn in “Margot at the Wedding” (2007) was, for many viewers, even more off-putting.

Yet despite such difficult protagonists, Baumbach’s films have a generosity of spirit. In “While We’re Young,” for example, it would be all too easy to satirize — or worse, dismiss — Driver’s and Seyfried’s hipsters. But it’s clear that Baumbach loves those characters, in a way, as much as Josh and Cornelia initially do.

Baumbach explains his curiosity by quoting the famous line from “The Rules of the Game”: “Everyone has his reasons.”

Such acceptance of our shared imperfection, he says, doesn’t come from upbringing or temperament, but from years of therapy. (Though Baumbach briefly saw a shrink as a teenager, he didn’t begin psychotherapy in earnest until his late 20s, after the release of “Mr. Jealousy,” a 1997 flop that ushered in what the director calls eight years of “struggle” before his next movie, “The Squid and the Whale,” an Oscar-nominated hit loosely based on his parents’ divorce.)

“Part of therapy is being able to acknowledge the darker aspects of yourself,” Baumbach says, “of the people around you, to understand yourself. Anybody who’s had any therapy kind of discovers fairly quickly that there’s a gap between your real self and the self you present to the world, no matter how self-actualized you are. That’s what the basis of all this is.”

In “While We’re Young,” Driver and Stiller play documentary filmmakers, the younger of whom exhibits questionable ethics that inflame Josh’s old-fashioned sense of truth in art — but also make him feel like a dinosaur. It’s tempting to read the characters as versions of Baumbach — Josh as close to the filmmaker’s real self, and Jamie a kind of youthful wish fulfillment).

For Baumbach, the characters of Jamie and Darby — though grounded, as are all of Baumbach’s characters — are not as fleshed out as Josh and Cornelia.

“What was fun for me about this story was thinking, in a way, of Jamie and Darby as almost like projections,” he says. “They could be ghosts in another story.”

In other words, they’re catalysts — leading to Josh’s ultimate epiphany about life, which comes late in the film. “You always go into therapy for one thing,” Baumbach says, “and then you realize you’ve got a whole other thing.”

That might make “While We’re Young” sound like medicine, but it’s not. Baumbach wants audiences to remember that the movie is very much a comedy. And that he’s still young at heart.

“I mean, come on,” he says, “the movie has a montage of people throwing up in it.”