Carl Reiner, the 95-year-old comedian, writer, actor, and director, has a running gag about life as a nonagenarian. “Every morning … I pick up my newspaper, get the obituary section, and see if I’m listed,” he explains. “If I’m not, I have my breakfast.” He stages a version of this routine for the new documentary If You’re Not In the Obit, Eat Breakfast, airing Monday night on HBO, in which Reiner and a handful of other 90-something personalities mull old age, and the possible reasons for their longevity. “Is it luck? Genes? Modern medicine?” he wonders. “Or are we doing something right?”

The result, directed by Danny Gold, is a documentary that’s loose, unfocused, and utterly charming—much like its subjects. Reiner wants to challenge perceptions about what it means to be living in your 90s (really living, rather than simply alive), and so he chats with friends who, like him, are thriving late in life. Tony Bennett, still swinging at 90, is filmed singing over the opening credits. The filmmaker Mel Brooks (90) and the TV producer Norman Lear (94) converse with Reiner about the impulse to keep working, as do the actress Betty White (95) and the actor Dick Van Dyke (91). The freewheeling, genial nature of the proceedings means the movie often feels like a Hollywood reunion, which perhaps explains why Jerry Seinfeld (a relative baby at 63) also pops up occasionally to ponder the potential of old age.

As far as science goes, If You’re Not In the Obit, Eat Breakfast is more interested in anecdotal evidence than it is in rigorous analysis of what might lead to greater quality of life later on. But what evidence there is is persuasive, simply because all of the movie’s interviewees appear to be having such fun. Van Dyke, who married a woman more than 40 years his junior, is particularly effervescent, dancing around his home, recording a new album, and espousing his lifelong habit of staying active. The pianist Irving Fields, who died in 2016 at the age of 101, is shown playing regular concerts at the Park Lane Hotel. “I could work nine days a week and not be tired,” he claims. “I go on and on because I love what I do.”

Perhaps aware of the fact that entertainers are a special breed, Gold also interviews a number of regular Americans who continue to blossom well past their 90s, and who assert the film’s general thesis that physical activity is paramount. These include Tao Porchon-Lynch, a 98-year-old yoga teacher, and Ida Keeling, a 102-year-old runner whose story is so inspiring it demands its own feature-length version. Keeling started running at the age of 67 after both her sons had been murdered. “I felt so different … like I had come out of my shell,” she explains. “Now, I’m chasing myself. There’s nobody to compete with.”

It’s in moments like these that Gold (and Reiner, who acts as a kind of emcee) really challenge perceptions about what growing old has to mean. Their subjects seem to view every day as an opportunity, rather than as another notch on an increasingly long calendar. “People are so worried about getting old,” the 95-year-old fashion icon Iris Apfel explains. “I never think about [it]. I think people should just take advantage of being alive.” Reiner, shown signing books for fans, posing for photographs, and doing stand-up shows, maintains that he’s busier and more productive than ever. Though, as he jokes to Betty White, not all aspects of aging can be helped: “You don’t lose interest in sex, but you lose your power.”

As a portrait of Old Hollywood (literally), If You’re Not In the Obit, Eat Breakfast is so endearing you might forget how revolutionary it is to propose that people in their 90s can still be creatively vital and physically vigorous. Certainly, it zips right over the economic disparities between its primary subjects and most elderly Americans, and the fact that it’s a lot easier to be determined to enjoy life if your life is enjoyable to begin with. But there’s still something inspiring about its argument that age isn’t an impediment. “This is the best part of my life,” says Jim “Peewee” Martin, a D-Day veteran who participated in a parachute jump in 2014 at the age of 93. “To me, vitality means you can do whatever you want, regardless of what the clock says.”