Weylin's point is valid. There is a concept in law of "proportionate response). For example, someone spits on your lawn and you shoot them, that is a reponse that is a little out of proportion. However, if someone attacks you with a weapon, you have the right to defend yourself proportionally.
Sometimes in the past the courts have said it's unfair to defend yourself with a gun when you are attacked with a knife, but deadly force is just that...deadly force. Doesn't matter if it is a broken beer bottle or a howitzer cannon, if you can make a case that you were threatened with deadly force, you can respond with deadly force.
In this case, I bet they gave the old guy a lecture and laughed all the way back to the stationhouse about how the kid filled his Fruit-of-the-looms.