Jennifer Garner and Christa Belle on ’13 Going on 30′ Turning 20 (Exclusive)

13 Going on 30 is saying goodbye to its teens! 

The Jennifer Garner-led romcom is celebrating 20 years since it “Thriller”-danced its way into theaters — and into the hearts of both nostalgic adults and kids who wish they could skip adolescence.

“It was magical,” Garner, 51, tells PEOPLE about her “many favorite memories” playing Jenna Rink, a teenager magically transported into her future self as a 30-year-old fashion editor. 

“It wasn’t a huge movie,” adds the actress. But for her, breakthrough heartthrob Mark Ruffalo, 56, emerging character actor Andy Serkis, 59, and supporting superstar Judy Greer, 48, “it was the biggest paycheck any of us had ever had, even though it was not crazy,” she recalls. “It was such a step up. We didn’t know if it would be any good or not, but we were all so in it to win it.” 

“13 Going on 30, in my view, will forever live on as both a rom-com classic and a cinematic love letter to the power of manifestation,” says Christa Belle, who played the younger, 1980s-set version of Jenna in the Gary Winick-directed film. Her favorite scene, of course: “The flash mob ‘Thriller’ dance scene will forever be my favorite.”

At 32, Belle is now older than grown-up Jenna — and has referenced the movie in the past on social media by celebrating her own 30th birthday and donning the character’s colorful Versace dress. Superfan Ariana Grande also honored the character with that iconic outfit, she notes: “I love that Ariana is a fan of the film!”

Women of all ages dressing up as Jenna for Halloween each year, adds Belle, is a testament to the movie’s enduring resonance. “I feel honored to share Jenna Rink with the world and I hope people dress up as her forever. We are all Jenna Rink.”

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Garner remains so close with costars Ruffalo and Greer that she barely remembers 13 Going on 30 is how they met — “That’s how deep we go,” she tells PEOPLE — and says any scene shared with either counts as a favorite. 

“The night that Mark and I shot in Brooklyn, looking back at Manhattan, the Razzle night,” she says of the scene where Jenna and Ruffalo’s Matty go out to buy the candy. “That is a favorite memory.”

As for Greer, “one of my girlfriends forever,” Garner notes that the actress spoke at her 2018 Hollywood Walk of Fame ceremony. “And then I spoke for Mark [at his ceremony this February],” she adds, “and then we’ll both speak for Judy when her turn comes — which is inevitable!”

The Alias star and her longtime friends “were just talking about the magic of all of us being at the same place in our careers” when 13 Going on 30 became a hit, she says. 

For Belle, one of the movie’s lasting impacts on her life was meeting Garner. “She treated me with such kindness and care, always,” remembers the actress — who Garner asked to play a younger version of her character again in 2009’s Matthew McConaughey romcom Ghosts of Girlfriends Past.

“I am grateful to have had such a wonderful experience with her so early on in my career as she has since remained a great example of a person with true character and integrity in Hollywood. The persona you see in Jennifer’s press is consistent with who she is in life, and I find that so refreshing,” Belle says. 

Fun fact: Belle also bonded with another costar whose career took off after 13 Going on 30. “At the time the film came out, AOL was a big deal and Brie Larson and I used to Instant Message from time to time.”