In Noah Baumbach’s “Greenberg,” there’s a scene where Ben Stiller, playing a prickly, neurotic 40-year-old, gazes fearfully at teenage kids around him at a Los Angeles party. “You’re so sincere and interested in things,” he sneers. “I hope I die before meeting any of you at a job interview.”

In Baumbach’s latest film, “While We’re Young,” that nightmare has come to pass. The backdrop for generational divide is just as much social as professional, but now Stiller is starring as half of a 40-something married couple (Naomi Watts is his wife) who befriend a much younger hipster couple (Adam Driver and Amanda Seyfried).

Stiller’s character, a documentary filmmaker who’s spent nearly a decade making the same film, becomes a mentor to Driver’s aspiring documentarian. While their age-appropriate friends are having kids, Stiller and Watts’ Manhattan couple take hip-hop classes, bike in Brooklyn, don questionable hats and generally try to pretend they’re still 25.

The two movies, “Greenberg” and “While We’re Young,” have established Baumbach and Stiller as a potent pairing. Stiller’s performances have been called among his best, and the films have contributed to a vibrant midlife period for Baumbach, who in between made the black-and-white 20-something comedy “Frances Ha” with his girlfriend Greta Gerwig.

“In both cases, thinking of Ben doing these things just made a lot of sense to me,” Baumbach said in a recent interview with Stiller. “If we keep making movies together, then I guess we can just finish off a life.”

“Go off into the sunset!” chimes Stiller.

“I wish I had gotten to Ben when he was 14,” adds Baumbach, imagining their version of Truffaut’s Antoine Doinel series.

“I could have given you some gold,” Stiller adds, cackling. “You should check out my head shot when I was 14.”

It’s fitting that the two have come together to chart the sometimes painful acceptance of adulthood. Back in the 1990s, the first film each made — Stiller’s “Reality Bites,” Baumbach’s “Kicking and Screaming” — were indelible portraits of what became known as Generation X. “Kicking and Screaming” came out shortly after the sensation of “Reality Bites,” which Baumbach cheerfully recalls, beat him to the generation-defining punch.

The two didn’t know each other until years later, “but we might as well have,” says Baumbach.

“We grew up in New York, obviously, with creative parents,” says Baumbach. “That and ‘SCTV.’”

They nearly crossed paths in the late ‘90s when Stiller’s brother-in-law was Baumbach’s assistant, but they only became acquainted when Stiller reached out to Baumbach after seeing his “The Squid and the Whale.”

Baumbach, knowing he wanted to work with Stiller again after 2010’s “Greenberg,” wrote the lead in “While We’re Young” specifically for him: “I wanted to write a comedy about a marriage and having Ben’s voice, or at least my interpretation of Ben’s voice in my head was very helpful.”

Stiller was receptive: “Ah Baumbach again!” he jokes. “Stop wanting to work with me on all your good movies!”

While Stiller’s character “Greenberg” was grouchily inert, unable to reconcile himself to unfulfilled ambitions, in “While We’re Young,” he’s game (maybe too much) to adapt. He marvels at how things that were once uncool (vinyl, VHS tapes, novelty songs) are now embraced by a younger, seemingly softer generation. Driver and Seyfried’s characters raise chickens and make artisanal ice cream.

One song in the movie, Lionel Ritchie’s “All Night Long,” epitomizes the adjustments of aging for the 45-year-old Baumbach. Though he hated it in the 1980s, he’s changed his mind: “I was reintroduced to it by a younger generation who had no association with it besides it being awesome.”

Though they very much identify with the film, Baumbach and Stiller, 49, both exude contentment with their place in life and in their careers. Stiller, after directing his first drama in “The Secret Life of Walter Mitty,” is next returning to a role he played almost 15 years ago: Derek Zoolander. He’ll direct the sequel, “Zoolander 2.”

“I’m excited about the idea of doing it,” says Stiller. “But there’s always that question: What the hell am I doing? What am I thinking making a movie 15 years after the first one came out that no one went to in the first place?”

The anxieties of such a gap sounds distinctly like a Baumbach plot. The continual struggle for self-redefinition through life’s stages make up the shifting timeline of his movies. Baumbach’s next one, “Mistress America,” deals with a character turning 30 played by Gerwig.

“I always feel like squaring yourself with where you are with where you thought you might be is interesting to me. I feel like it’s human,” says Baumbach. “There are darker aspects to that and there are lighter aspects to that.”