Just remember that next time he WILL bring a gun and some of his friends who have guns WILL bring theirs and they just won’t rob you, they will kill you.
Here is a NY Slimes report to corroborate the above.
Common criminals are cowards, they already know I am armed, so I doubt they would come back for a second chance at robbing an armed man.
Sorry, but most teenagers aren't hard core criminals who would come back for a revenge killing.
That's the chance I'd take before shooting an unarmed teenage running away from me