User blog comment:Merganafan23/Character ages/timeline/@comment-109.148.87.100-20130930144014

Season 1 starts exactly 20 years after The Great Purge ended, and Balinor fled Camelot

Arthur was born at the start of The Great Purge.

Merlin was born after The Great Purge as his farther was Balinor, who fled Camelot.

Arthur turns 21 in season 1 episode 9 Excalibur.