Dawson Casting: Given the vocally and physically demanding roles, the sexually explicit content, and the fact that the main characters are all around 14, this was inevitable. The ultimate example has to be the 29-year-old Andy Mientus playing 14-year-old Hanschen, followed by the 28-year-old Alex Wyse as Georg.
Averted by Lea Michele in the workshop productions.
Averted by Jennifer Damiano in the original Broadway cast, who was fifteen when the show opened (and was actually supposed to understudy Lea as Wendla until the show found out they couldn't have an actress that young perform in a sex scene.)
Romance on the Set: The main cast is played by a bunch of college-aged kids who spend all their time together! This was bound to happen. Numerous pairing have been linked throughout the show, special nod to Christy Altomare (Tour Wendla) and Gerard Canonico (Broadway Moritz) who met through Spring Awakening but were never in the same cast.
In the revival, Andy Mientus (Hanschen) and Michael Arden (the director) are engaged.