Is 90 the new 40?

If the new HBO documentary “If You’re Not in the Obit, Eat Breakfast” is any indication, the answer is a resounding yes.

The title of the film, which premieres on the premium cable network on June 5, is based on an old joke of 95-year-old Carl Reiner. Reiner has been incredibly busy since he turned 90, writing several books and is active on social media. He even tweets an anti-Trump story before he goes to bed at night.

In the film, he tries to find out why so many people are defying their age and leading vital lives after the age of 90. He visits with Dick Van Dyke, 91, who became a star in Reiner’s Emmy Award-winning 1961-65 CBS sitcom “The Dick Van Dyke Show.”

Van Dyke still sings and dances — frequently with his younger wife, Arlene — and just finished a role in the new “Mary Poppins” remake.

Equally active is his good friend, Mel Brooks, 90, whom he met over 60 years ago on the groundbreaking NBC comedy variety series “Your Show of Shows.” Brooks, the Oscar-winning writer/director of such comedy masterpieces as 1968’s “The Producers” as well as 1974’s “Blazing Saddles” and “Young Frankenstein,” has the energy of a 60-year-old.

And 94-year-old award-winning producer Norman Lear (“All in the Family”) is enjoying the success of the Netflix reboot of his comedy series, “One Day at a Time,” with a Latino cast.

Reiner also checks in with Betty White, 95, as well as Kirk Douglas, who turned 100 this past year. The film also shines the light on such non-celebs as 102-year-old track and field athlete Ida Keeling and 96-year-old World War II paratrooper Jim “Pee Wee” Martin, who parachuted on the 70th anniversary of D-day.

Tony Bennett, 90, opens the film with “The Best is Yet to Come” and the documentary concludes with Oscar-winning composer Alan Bergman, 91, performing “Just Getting Started.”

As funny and charming as “If You’re Not in the Obit, Eat Breakfast” is, it didn’t hold a candle to the post-screening Q&A Wednesday evening at the Samuel Goldwyn with Van Dyke, Reiner, Brooks, and Lear, hosted by Tom Bergeron of “Dancing with the Stars.”

No sooner had they taken their seats on stage, Brooks stood up and told the the crowd: “Ladies and gentlemen, the greatest cat sound in the world,” he proclaimed breaking into the loudest yowl.

Longtime talent manager and producer George Shapiro poses with Carl Reiner after the screening. Lauren/Variety/REX/Shutterstock

The audience started howling. “What the hell do you want?” he quipped. “You’re not paying a penny here.”

Bergeron asked Van Dyke if he felt 91. “You don’t act 91,” he noted.

“No, I don’t,” said Van Dyke. “I feel as good as I ever did. I am one of those who wakes up on the right side of the bed. I realized that’s not a habit you can acquire. Your brain chemistry is that some people just get up on the wrong side. I get up and I’m talking and nobody wants to hear me.”

“I wake up and take a leak,” noted Lear, prompting Bergeron to say, “There you go. It’s always better to get out of bed to do that.”

The documentary features several clips of Reiner and Brooks’ legendary routine of “The 2,000 Year Old Man.”

Reiner noted that the routine began “because Mel was the funniest human being in the world. When I came to work on ‘Your Show of Shows,’ there were writers in the room. Mel was there as a friend of Sid Caesar’s. He worked with Sid, not for [producer/director] Max Liebman or the show.

“I walked in and I didn’t know who he was, but he was standing there doing a Jewish pirate. The first words out of his mouth he says, ‘You know how hard it is to set sail today? You know what they are charging for sail cloth? I can’t afford to pillage.’”

The following Monday, Reiner walked into the office. “I had heard ‘We the People,’ a television show about current news. I turned to him for no reason and said, ‘Here’s a man who’s 2,000 years old. May I ask you a question? Did you know Jesus?’”

“He says, ‘Thin lad? He wore sandals and walked around with 12 other guys. They always came into my store. Never bought anything. I gave them water. The funniest brain in the world, and he still wants to do a cat noise. Would you do another one?”

“Yowl,” Brooks screeched.

(Pictured above: Norman Lear, Mel Brooks, Alan Bergman and Dick Van Dyke)