Grease became one of the world's most-loved musicals when it was released in 1978.
The film, which starred the late Olivia Newton-John and John Travolta, featured incredibly catchy songs and iconic fashion.
Most of the actors had parts in the stage version of the movie and simply took on new characters when they took on the feature film.
Cast members, including Stockard Channing, Jeff Conaway and Barry Pearl, went on to have fruitful careers in Hollywood.
However, fans of the movie noticed that many of the stars were a lot older than the highschool characters they played.
Was Michael Tucci, who played Sonny, really of high school age?
Olivia, who recently passed away at the age of 73, previously revealed she almost turned down the role of Sandy until John stepped in.
Writing in her autobiography titled Don't Stop Believin', the Australian actress revealed the moment she was offered the role - and the reasons she almost turned it down.
Producer Alan Carr believed she would make the perfect addition to the movie's line-up.
In her book, she wrote: "I was 28 and John 23. I couldn’t play a high school student at 28.
"“I’m too old for Sandy,” I told Alan. “And I can’t do an American accent.” He would change the script to make Sandy an Australian transfer student. Wow, they were really trying to make this work for me. But I was still hesitant."
John, who was 23 at the time of the movie, still captured viewers' hearts around the world.
Meanwhile, Stockard, who played Betty Rizzo, was 33 years old when the movie was being filmed.
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She was one of the oldest cast members.
Jeff Conaway took on the role of Kenickie, who was Rizzo's love interest. He was 26 at the time of filming.
He did star in the broadway version years before and would have been closer to his character's age at the time.
Marty Maraschino, who was played by Dinah Manoff, was the second youngest cast member and was 21.
Sonny LaTierri, a member of the T-Birds, was supposed to be 18 years old. The actor, Michael Tucci, was actually 31, making him the second oldest cast member.
Frenchy, who accidentally dyed her hair pink in the movie, was played by 26-year-old Didi Conn.
Meanwhile, Doody was played by Barry Pearl - who was 27 at the time of filming.
Jan, a high school student who rocked iconic pigtails, was played by Jamie Donnelly. The actress was actually 30 years old.
And of course, who can forget Putzie? Kelly Ward took on the role of the clumsy T-bird and was actually the youngest cast member, He was 20.
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