Board Thread:False Info and Speculative Discussion/@comment-98.21.154.70-20140718152310/@comment-19765459-20140718184316

The Hale House fire happened 6 years before the start of S1. Derek was in high school at that time, although he appears to have been an underclassman. Especially since his sister Laura (slightly older) was also in school. Unless Derek was an academic prodigy (highly unlikely based on what we have seen of Teen!Derek) he was probably 15 or 16 when the fire happened. That easily puts him into his early-20's at the start of S1.

This would be a rather different sort of show if Derek were the protagonist. Especially since he acts older than he is.