If I were this guy the 23 year old would never have gotten close enough to punch me in the face before he had a hole in him
He was warned, at least twice, and shown the defensive capability that would be used.
Stupid dead 23 year old is all I see here.
The older guy showed the kid he had two weapons: His own strength and a GUN. He made it pretty clear that he would probably fall back on the latter if the kid chose to escalate. He did, and he did.
Never bring a fist to a gunfight.