It’s an old joke in Hollywood that the actors who are cast to play high school students are very rarely teenagers when the show or movie is filmed. Riverdale, The Society, and 13 Reasons Why are a few recent examples that all depict much older actors trying to channel their inner teen on screen. Netflix seems to be particularly fond of this casting trend considering Noah Centineo has portrayed a high school student in three of its films despite being 23.
The cast of Netflix’s latest show Trinkets, includes Quintessa Swindell, Kiana Madeira, and Brianna Hildebrand of Deadpool fame as three high school girls who bond after a Shoplifters Anonymous meeting, also follows this trend. The drama series depicts their friendship as well as the different social circles they fall into at their high school. Most of the characters are teenagers, with a few exceptions (ahem, love interest Luca), but not a single cast member is an actual teen.
Still, the casting choices here make it very easy to understand why these actors were chosen for their specific characters. Most of them are in the their 20s and most of them are folks you've definitely seen on screen somewhere before.