In the HBO series Euphoria, Zendaya delivers a bravura performance as Rue Bennett, a 17-year-old high school student and recovering drug addict. Zendaya’s performance is all the more remarkable because she has never used drugs—not even booze—nor did she have a typical high school experience, whatever that might be, having been a celebrity since she was a teen. She’s also 26, a bit long in the tooth for a high school junior. Or is she? Certainly not in TV shows or movies, where it’s fairly common for actors to play teenagers well into their 20s and even 30s. In case you’ve forgotten any of them—like Andrew Garfield’s turn as a teenage Spider-Man (27!), Stacey Dash as Dionne Davenport in Clueless (28!) or Stockard Channing playing Betty Rizzo in Grease (33!)—there are nu...