Most egregious cases where a clearly aged actor plays a teenager

We all know that Hollywood has a tendency to cast older actors in teenage roles. But what's the most egregious example of this?

  • Literally the entire Grease cast. Excellent movie. But quite literally none of them look and sell me as teenagers in high-school, especially John Travolta.
  • Saoirse Ronan in Lady Bird. She had a sublime performance, but I don't think she really looked the part for a high-schooler.