Do you think the teens would've run out of the house if he didn't show up with a gun shoting them? Would they push him, hit him? Would they maybe even kill him? Where they influenced by alcohol? Drugs? What? Did the teenager have weapons? What are they breaking into his house for? There's so many possiblites - Regardless of them, you're ending up making a mistake. Let's say we come to the possiblity - He goes without a weapon and confronts them, they're influenced with drugs and alkohol and try to somehow attack him. Scenario would be - teenager broke into a seniors house and killed him - Now then you would say - He should've taken proper mesurements. Confront them with weapons etc, call the police w/e.
We're talking about lifes. Always sad to that lifes go away but don't take one part of the case. It's not about the money, it's about the lifes. We don't know what would've happend if he wouldn't have confronted them with a gun. Some things can't be taken by chances. Even having the gun pointed at them. How could a man at age 60-70 think that they didn't have any guns, or knives? He at that age is slow and could've been surprised easily.