What's the Role of Legislatures in Determining Age Appropriateness?

Who is the appropriate person or institution to determine age appropriateness? Right? When i watched schinder schindler's list when i was in high school, i had to take a form home to my parents to get it signed. The same question can be asked of who determines what gets taught with in the curriculum in schools. This isn't a new debate, right? It goes all the way back to the scopes monkey trial in 19 20.