“I believe age should be celebrated and revered,” the legendary supermodel, who celebrated the milestone birthday on Tuesday, told Page Six Style. “There’s a reason we have cakes and parties on our birthdays, and I feel the same way about getting older each year.”

But even Schiffer — who over the course of her decades-long career has appeared on more than 1,000 magazine covers and strutted countless runways — has fashion regrets.

Growing up, she said that her “very ’80s” look revolved around “stonewashed high-waisted jeans from Chipie, oversized sweatshirts from Fiorucci, blue eyeshadow and lots of hairspray.” These days, she sticks to classic denim paired with sweaters or blouses, a uniform she says “feels effortless, but can take [her] from the school run to meetings and on to dinner with friends.”

Enter the blond beauty’s latest project, a collaboration with celeb-loved denim brand Frame on two new limited-edition styles launching on Friday: a light-wash skinny jean ($220) and a wide-leg black pant ($225), each featuring a back leather patch adorned with a cloud as a nod to the star’s nickname, “Cloudy.”

“You can never go wrong with a skinny or wide-leg, no matter how you style them,” Schiffer said of the two pairs, a portion of the sales from which will benefit Unicef. “I wanted to design denim that looked polished and effortless — silhouettes that anyone could easily dress up or down.”

More than being just an everyday outfit essential for Schiffer, denim has played a starring role in her career. Back in 1989, she got her big break as the star of Guess Jeans’ black-and-white campaign, which was photographed by fellow German up-and-comer Ellen von Unwerth and inspired by test shots the pair took together in Paris.

“She was starting, I was starting. We got on like a house on fire, having fun, being silly, just mucking around next to the Centre Pompidou in my own clothes,” Schiffer recalled. “Cut to Paul Marciano, who saw the pictures and wanted us for Guess Jeans.”

A fragrance ad for the fashion brand followed, as did whirlwind trips around the globe for photoshoots, TV appearances and more. “I remember flying around the US to every major city for signings in department stores with massive crowds — only to be interrupted when a duck flew into one of the engines of Ron Perelman’s private plane, which caused a fire and an emergency landing,” Schiffer said of one particularly memorable trip.

The supermodel also credits the late, great Karl Lagerfeld with helping make her a household name. “I’ll never forget meeting him for the first time when I was 18, at a fitting in his studio in Paris on Rue Cambon. He had seen my British Vogue cover by Herb Ritts and asked that I come in,” Schiffer explained.

“Before I knew it, I was being fitted for his new collection — and then the next day I found myself driving to Deauville to shoot my first Chanel campaign, photographed by Karl,” she continued.

“I remember us bonding over the fact that we were the only two people full of energy at 3 a.m. in the morning. In his case, he was always full of energy; I was just full of adrenaline and loving every second of working with him.”

When Lagerfeld died in 2019, Schiffer was among the first stars to mourn the fashion legend on social media. “Karl was my magic dust, he transformed me from a shy German girl into a supermodel,” she wrote on Instagram, calling him “irreplaceable” and “the only person who could make black and white colorful.”

She continues to pose for Chanel campaigns to this day. And in addition to her collaboration with Frame, she’s been flexing her creative muscles by curating an exhibition of ’90s fashion photography for the Kunstpalast in Düsseldorf — the city where she was first discovered — which is set to open in March 2021.

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“I’m very lucky to love what I do and to be able to pick and choose my projects with partners that I admire,” she said. “I’m enjoying the different avenues my career has taken, including roles where I am designing or curating collections, which felt like a natural next step for me.”

But whether she’s in front of the camera or behind it, one thing’s for sure: Schiffer won’t be stressing about her appearance as she enters her next decade.

“I don’t try to look or feel younger; I embrace the now,” she told us. “If you’re happy and healthy, the rest will follow — and as Michael Caine said to me, aging is much better than the alternative option!”