When you're dealing with the older ages - someone in their 50s, say, and then someone in their 70s - it's just a lot harder to find two actors who are similar. When you get into younger people - the teenager to someone in their 30s obviously, people can change a lot in that time.
You'll always want to find an actor in the larger role first.
It's double casting, because there's twice as many people. The episode I'm doing now has seven matches.
