Shirley Henderson made a memorable entrance into the magical world of Hogwarts as Moaning Myrtle in Harry Potter and the Chamber of Secrets. 

Despite being 37 years old at the time, her portrayal of the 14-year-old muggle-born witch made her a standout performer in the franchise.

When Grease hit the big screen in 1978, it was a high school musical like no other. 

Audiences fell in love with the antics of Rydell High. But here's the twist—those "teenagers" were more suited for a reunion than a prom! 

John Travolta, aka Danny Zuko, was 23 when the movie was filmed, and he was younger than most of his other castmates. Meanwhile, the late Olivia Newton-John, who played the beloved Sandy, turned 29 while filming Grease. She was about a decade older than her character’s age.

The biggest surprise? Stockard Channing, the sassy Rizzo, was a cool 33 and the oldest of all the main characters of the film.

“[Producer Allan Carr] showed up on the set with a brown pencil and started dotting freckles on my nose so I would look younger,” Stockard told Vanity Fair. “I said, ‘I don’t look younger! I just look dirtier!’”

Actor Jeff Conaway, who played Rizzo's love interest Kenickie, was 26 at the time.

Henry Winkler's portrayal of Arthur "Fonzie" Fonzarelli in Happy Days became iconic despite him being 28 when he landed the role.

His cool demeanor and leather jacket made him the epitome of cool, resonating with audiences and earning him a permanent place in TV history.

His character was such a massive hit that the makers of the show considered changing the title to “Fonzie’s Happy Days,” but Henry dissuaded them.

Henry only realized how famous he was when he asked for his fan mail to be sent to his apartment, leading to 50,000 of them arriving at his address.

“Box after box, and I read them all,” he told The Guardian. “Some of them were just a sentence in crayon, others were so dear and thoughtful.”

In Mean Girls, Rachel McAdams played the iconic teenager Regina George with chilling perfection despite being 26 at the time. Her portrayal of the high school queen bee was so convincing that it was easy to forget she was a few years older than her on-screen peers.

Lindsay Lohan was 18 when she played 16-year-old Cady Heron, Lacey Chabert was 21 while playing Gretchen Wieners, and Amanda Seyfried was 19 while playing Karen Smith.

In Pretty In Pink, James Spader brought a dose of adult sophistication to his high school role as the suave and scheming Steff. 

At 26, his portrayal of a privileged teenager felt more like a seasoned professional crashing the prom, adding an extra layer of intrigue to the teen drama.

The list would be incomplete without a mention of Tom Welling's portrayal of teenage Clark Kent in Smallville. The actor was 24 when the show began, with his character, Clark, being 14 years old.

A decade of Clark’s journey was covered in the show, by the end of which Tom was about 32 or 33 years old, while his character was about 24 to 25 in the final episode.

Several members of the Beverly Hills, 90210 season 1 cast were notably older than their high school characters.

The most interesting casting choice was Gabrielle Carteris, who was 29 when the first season of the hit show premiered. As she played a character at least 13 years younger than herself, she crossed her 30-year milestone birthday during the season.

Most of the cast members in Clueless were remarkably close to the ages of their characters, adding authenticity to the high school setting. Alicia Silverstone was 18 when she played 15 or 16-year-old Cher, and Brittany Murphy was 17 when she played Tai, the teenage newcomer at school.

Donald Faison had turned 21 when the timeless rom-com came out. Meanwhile, Elisa Donovan was 24 when she played Amber Mariens.

The oldest of the high school gang was Cher’s best friend, Dionne, who was played by Stacey Dash when she was 28 years old at the time. 

Maggie Grace brought an unexpected twist to the Taken series, portraying Bryan Mills' teenage daughter, Kim, with a blend of vulnerability and resilience. Despite being 25 when she first took on the role, Grace convincingly channeled the wide-eyed innocence and teenage angst necessary for the character. 

At 29, she returned for Taken 2, where her character was still trying to pass her driving test, and she returned as Kim for Taken 3 around the age of 30.

Florence Pugh makes for one of the most compelling entries on the list of actors playing characters much younger than their actual age.

In Little Women, the actress was 23 years old in real life when she captured the youthful spirit of Amy March, who was only 13 in the movie.

A crucial must-mention in teen dramas is The O.C., which aired from 2003 to 2007. A number of cast members were significantly older than their characters’ actual age.

Ben McKenzie, in particular, was 25, and his character was 16 when the show began. Adam Brody, playing 16-year-old Seth Cohen, was 24 at the time, while Rachel Bilson, playing Summer Roberts, also 16, was 22 in real life.

Saoirse Ronan was 23 years old when she played the titular 18-year-old character in the 2017 film Lady Bird.

She won the Golden Globe award for Best Performance by an Actress in a Motion Picture -- Musical or Comedy for the same role.

The Oscar nominee said she could “relate” to the identity crisis that Christine “Lady Bird” McPherson goes through in the story.

"It’s something that every teenager goes through, where they’ll try on different characters and try to emulate the grownups around them and see if it fits…" she told Bustle in 2017. "I knew what that was like, because I actually did that, and would go from being the showman and the comedian like Lady Bird is to someone who’s insecure and lacks confidence... I think that’s just imperative for being a person, really, not just a young person."

Several older actors were cast as teenagers in The Fast and the Furious: Tokyo Drift, and the most stark evidence of this was Lucas Black’s appearance in the 2006 racing movie. He was 24 when he played Sean Boswell, making his high school student persona a tough sell. 

His mature look at the time made it hard to believe that he was a “high school teen” making reckless decisions as he drifted through high school.