At 17 years old this guy knows better. 13 years olds do silly things for kicks. This kid is 6 months away from being in a nuclear submarine (argument for another day).
I fully agree that killing him was too far. I wouldn't have done it. Shooting him in the kneecap though will have you up paying medical bills for the rest of their life. And we know what that costs!
I feel that you give up your basic human rights the second you create malicious intent for another person. My personal values are set at STEALING my car or from my home. Anything else and I would never physically harm someone. Now, if a person breaks into my house (even without a gun), I'm giving them a 3rd eyeball. Period.