Jesse Heiman is in his 40s and still playing teenagers or 18-22 year olds
Also John Leguizamo is in his early 60s and has pretty much made a career out of playing people a decade or so younger than himself. Some notable examples include that he was in Hangin' with the Homeboys at 31 and played someone who was around 18-22 (they talk to his character several times like he's someone who recently graduated High School) then did Super Mario Bros at 33 playing a Luigi who seemed to be 23. Also he was 36 and 37 when he did Romeo+Juliet and The Pest and played twentysomethings in both those movies.