In the new film “Mack & Rita,” 30-year-old writer Mackenzie “Mack” Martin (Elizabeth Lail) longs to unleash her inner 70-year-old. Wearing her best friend Carla’s (Taylour Paige) thigh-high stiletto python boots — because her own clothes are unsuitably frumpy for Carla’s Palm Springs bachelorette party — Mack totters into a tapestry-laden tent advertising past life regressions. There, aided by a huckster in a caftan (Simon Rex), she lays down in a repurposed tanning bed and channels her inner self.

“I don’t wanna have to pretend I like kombucha. I don’t! It’s disgusting! I want to be free to say whatever I want,” she wails. “I’m a 70-year-old trapped in the body of a 30-year-old who just needs a minute to rest!” On that last line, Ms. Lail goes full Diane Keaton: eyes wide, hands splayed, shouting from her comic depths.

Wind blows, chimes tinkle and Mack emerges from the magic tanning bed as … Diane Keaton.

If “Big” and “13 Going on 30” painted our 30s as one’s prime, “Mack & Rita” poses another option that’s particularly resonant in 2022, with Ms. Keaton as its poster girl: our 70s. It also offers a portal to something deeper: a current collective wish to fill our kitchens with hydrangeas, drape ourselves in Eileen Fisher, pour some wine over ice with our closest friends and stop sweating the small stuff.

This spring, TikTok-er Lex Nicoleta hit a nerve when she coined the term “coastal grandmother” for the luxuriously relaxed aesthetic Ms. Keaton helped popularize nearly two decades ago in the Nancy Meyers movie “Something’s Gotta Give.” Ms. Nicoleta’s TikToks went viral and spurred countless guides for getting the look (including one by this newspaper), which includes easy-fitting white button-down shirts, straw hats and cardigans ranging from greige to beige.

Now, as summer winds down, Jimmy Fallon and Jane Fonda have released a music video tribute to the style and Nantucket homeowners are reportedly updating their décor to attract millennials in search of #cottagecore — another “trend” that’s been lurking beneath our eyes for decades, if not centuries, with its white-hot gingham and chintz table linens, floral-painted pottery and old wooden furniture.

“Look, I was not really somebody who was aware of the coastal grandmother situation,” Ms. Keaton said by phone on the day of the film’s premiere. “I kind of live my life, not singular, but with a few friends and my family, and also all the interests that I have.”

“Being in my 70s, it’s understanding more about how profound love is,” she added. “Instead of being, you know, busy.”

Which of course is what makes Ms. Keaton, at 76, aspirational to people of all ages. Deep down, it’s perhaps less about open-plan kitchens and cashmere knitwear than a desire to release a well-earned exhalation and be oneself without apology.

For those fortunate enough, the pandemic, with its sudden absence of a bustling work culture or packed social calendar — and a sudden sense of mortality — offered an opportunity to play at this, and prioritize their home lives, close relationships and time in nature. Whether or not they wanted to return to the office is one thing; they might have just wanted to keep living like retirees regardless.

But the last two-plus years have also affected the mental health of many millennials and members of Gen Z, disrupting their formative years of school and early workplace experiences, and isolating them during a period usually devoted to forming strong social ties. That’s not to mention the political polarization, confounding economy and climate crisis they look forward to inheriting.

For some women in the U.S., a hug from grandma sounds great, but maybe being grandma sounds even better. Especially if she looks like Ms. Keaton, which is to say, accomplished, beloved, healthy and wise — with or without a man.

Paul Welsh and Madeline Walter, who co-wrote “Mack & Rita” in 2018, said the idea was born one Monday morning when, instead of working, the pair was espousing the virtues of Burt’s Bees eye cream and the British crime drama “Broadchurch.” The writers realized their interests were skewing senior, and they were not alone.

The film “was honestly the answer to conversations that, as people in our 30s, we were hearing people around us having all the time,” Mr. Welsh, 39, said at the premiere at NeueHouse Hollywood.

“There was this collective exhaustion of people who were a little burnt out on the idea that you have to strive or have to be competitive,” Ms. Walter said. “So what would a wish fulfillment movie look like where someone wishes to be old? It’s not a punishment. It’s nothing to be afraid of.”

Ms. Keaton’s character, along with her newfound “wine club” of gals her age (played by Loretta Devine, Amy Hill, Wendie Malick and Lois Smith), makes the AARP status look eminently appealing — even fun.

“We’re like the Greek chorus,” Ms. Malick, 71, said of the group. She said the joy those characters found in each other’s company felt true to her own life. “You have to have a really good support system of women that can get you over the humps of life with a great sense of humor.”

She added, “I have a group of girlfriends and we all figure we’ll probably outlive our mates because a lot of them are older. We always think about where we will go live in commune together with our chosen sisterhood. And we’ll let men come visit, but then they have to leave.”

The movie also gets at a truth that many feel that our physical age may not necessarily reflect our inner spirit.

“My spirit age is a solid mid-30s, with a heavy shake of the elderly,” said Ms. Walter, who is 37. “Once in high school I walked into a class that was my class, and someone thought I was a substitute teacher. And I love soup. I am obsessed with soup.”

“I think mine is younger,” said the film’s director Katie Aselton, 43. “I don’t know if it’s because I have teenage daughters.”

“It was interesting making this movie, where I had one leg, truly, in with the younger generation,” Ms. Aselton said. “I feel these insecurities. I feel all of the pressures of society. And then I had one leg over with the older ladies being like, ‘Yeah, but if you just let it all go, and be free, release it, own yourself, be you.’”

Ms. Paige, 31, said her spirit age feels similarly split. “It’s like I’m either 7 or I’m 93,” she said. “I’m pretty basic and simple in what it is I want out of life, which I feel like is an older person, but I’m very much, like, alive and trying to take in all that I can and wanting to jump on my bed and do cartwheels.”

“Mack & Rita” costume designer Allyson Fanger, who also dressed Ms. Fonda and Lily Tomlin for their Netflix show “Grace & Frankie,” said many of the hallmark hats, turtlenecks, wide belts and full skirts Ms. Keaton wore in the movie were the actor’s own. But other items, including those unforgettable python boots, had to be acquired in multiples for both Ms. Lail and Ms. Keaton.

Asked whether she was hanging onto them, Ms. Keaton let an enthusiastic expletive fly.

“Excuse me,” she caught herself. “I’m going to say it this way: Yes! You never know when you can use them.”