Just got his driver's license!

To be fair, Grease is a parody, and that was part of what they were parodying at the time. So they went a little extra with it too.

It's a parody of the super common "beach fling" style of movies from the 60's. They even reference some common actors and actresses from those movies.

It's why each scene seems so poorly tied together, and the characters aren't very consistent.

Like the whole final number with Sandy in full leather suddenly being the sex asker.
- "Tell me more, tell me more
  Did she call the police?"

Sometime the reverse is true.

Keira Knightley had just turned 18 when she filmed Love Actually (2003). She played a newlywed woman in her mid to late twenties. Her famous "floppy hat" was used because she had a giant teenager zit on her forehead.

Sometimes the casting is dead on.

Mariel Hemingway was 16 when she played the 17 year old love interest to Woody Allen's 44 year old man in Manhattan.

I think, in movies, a big driver in casting is trying to guide the audience. Had they cast actual teenagers in Grease, the audience would have been scandalized by the subject matter rather than focus on the comedy and music. That's why they cast a teen to play a teen in Manhattan. The entire thing is meant to feel off and uncomfortable, which would not have been apparent had they cast a woman in her mid twenties. They cast a teen Keira Knightley because they needed the audience to instantly understand why the character had a crush on her. Whether we like to admit it or not, our monkey brains register teen women simultaneously as angelic/pure and "peak breeding material" (yes, it's yuck when put that way).

Movie magic is built on multiple layers of subconscious manipulation.

Even with the casting choices, I'm flabbergasted that Grease became a cult classic. As far as I can tell the overall message of the film is: "if a woman wants to keep her man, she must act like a dirty slut."
- Didn't Travolta's Greaser character turn clean-cut in order to be with her? I always thought the point was that they originally liked each other for who they were, without pretense but society was forcing them to conform to standards and pigeonhole them.
  
  Or maybe it was all about the dancing and singing and we are trying to get too deep into it.
- To be fair, people don't really watch musicals for their plots.
- Yea and that "Did she put up a fight?" line in Summer Nights always creeped me out.
Odd question: there's an IT Crowd joke about Keira Knightly being in a movie where she was stabbed in the face, is that based off reality?

Just like my boy Jotaro Kujo

That's just Japan being Japan. Every JRPG ever ''He's a grissled war veteran that lost a civil war in his country and then fought in the war for our county, betrayed by his brother and framed as a traitor he's long been forgotten by everyone rotting away in an isolated prison cell'' Blood Type A, age 19.
- Oh and he lives alone and his apartment is massive and overlooks the waterfront, which is somehow in downtown Tokyo

So is the dude next him. Neither are passible.

Lol, that dude is John Travolta
- Yes, that's the point.
- He was 24 when Grease was made.
  
  The guy next to him is Michael Tucci, who was 32 at the time.
  
  Luke Perry at the beginning of 90210 was the same age as Travolta. Then later on the same age is Tucci in the same series.
- Yea and he is like 23 iirc when filming that. Don't get me wrong that other guy is probably older, 23 isn't terrible for an actor playing a teen. But he does not look like a teenager.