All of the "high school" kids are actually college age or older.

Has to do with child labor laws.

It's acting. They can all pass as high school students, so what's the harm? I seriously doubt anyone is going to start treating college students like high school students, whatever that means, after watching Stranger Things.

I don't see the problem. Seniors in high-school are generally 18 years old. Someone in their early 20's are not that far removed from high-school. They picked great actors/actresses for all the roles. Not like they're 30 years old.

They don't want to show actual teenagers having sex on screen, so they decided to use older actors...

Also, it is common for shows to use early 20s actors as teens, since it makes the teens look even more sexually developed and if the show goes on for longer their looks don't change drastically in a period of months or a year...

Also, 20 year olds today probably only look like late teens in the 80s, as the 80s had a more adult feel than the very infantilised times we live in now... 😉

It's a common trick of the trade used in show business. People like actors that look younger than they really are, so they can have them play younger roles, but have the maturity and reliability that comes with an older age. This is done all the time, where the actors playing kids or teenagers are actually much older than their character. It's especially helpful that for a lot of young adults, there actually isn't much physical changeover from high school to college during the first few years, beyond changing hair and clothes. There are also some people who have a genetic trait that we in the vernacular call being "baby-faced," where they look younger than they really are. Some examples would include:

- Billie Burke playing a seemingly ageless [20/30/40-something] Glinda in "The Wizard of Oz" when she was in her 50s

- Gary Burghoff playing a 19-year-old Radar on "M*A*S*H" in his 30s

- Michael J. Fox playing a teenaged Marty McFly on "Back to the Future" in his late 20s/early30s

- Jennifer Lawrence playing a 16-year-old Katniss in the first "Hunger Games" movie when she was 20

- Kirsten Storms playing a 13-year-old Zenon in "Zenon: Girl of the 21st Century" when she was 15

- Melissa Joan Hart playing 16-year-old Sabrina when she was already in her early 20s when the tv show started

- the little boy actor in "Heaven Is For Real" playing a 4-year-old child, when he in fact is 6

Sadly, not all film/tv makers are good at choosing young-looking actors, if that awful film "Grease" is anything to go by. They also play on the fact that most viewers are not experts in what people of certain ages look like.

Maybe it's a throwback to the high school/college movies of the 80's. When the actors played teenagers but were in fact closer to 30.

There's nothing new about that. I could pass myself off as a teenager well into my late 20s.

Some have played high schoolers even though they were in their thirties!!!