A teenager's mind is still very much in-development, so it can still be reformed. I don't think they should have a death penalty for teenagers, I'd rather they just rehabilitated them.

True, once they get to the point of torturing small animals at around the age of 17-18, I'd say there's a pretty small chance of getting them back. I've read places that one of the most common causes of psychopathy is abuse or neglect during childhood. Once you've made it to age 17-18, you're through with childhood; your mind is developed, but there's a big empty gap where the loving parents are supposed to go, and now it's too late to fill it.

They should probably atleast TRY to rehabilitate them, show them some love and how parents are supposed to be, and if that doesn't work... well, they've gotta go somewhere.