Would not turn my back on the guy let alone shoot with him. Nobody gets on my range that has a malicious pointing of a firearm in their past. I don't even allow friends on my shooting area who can't tell me the four rules for gun handeling. No way I stand anywhere near a person who has shown to be reckless in the past.
And you were never reckless or stupid when you were 17? I guess you get to throw the first stone then. People have the capacity to learn, grow and change for the better. But they need encouragement and positive reinforcement to make those changes stick. Ostercising them for past mistakes only causes them to give up hope that their change makes a difference.