Nah! I would go with an adolescent rescue. That way you can see toy drive, you can see temperament and you don't have to wait as long! I rescued Zuma around 10 months and it was perfect timing for sports.
To be honest, the majority of disc dogs out there are rescue dogs. As a community, it is really pro-rescue, which is great!
As long as you are jumping your dog smart and not playing over your head, there aren't very many injuries at all! Injuries happen when handlers have poor throws causing the dog to land bad, or if the dog just doesn't know how to jump/land properly. Or when people push their dog beyond their capabilities. So just be smart.