When did Hollywood stop using people well into their 20s to play teenagers?

When I grew up in the 80s and 90s, high school teens were played by people well into their 20s. Sometimes they played even younger teens. It always looked strange to me, even when it was the norm.Today kids play kids, teens play teens. It gives a much more naturalistic feeling to films. When did this shift happen and do we know why it wasn’t always like this? via /r/movies https://ift.tt/3JlHg8Y