I don't think it is right to kill anyone, but I don't think you can blame someone for defending themselves either.

In my opinion, if a person violently entered your home, it shouldn't be punished with jail time if you kill them.
You can't be at fault for not willing to risk your's and your families lives.

Old dude shouldn't go to jail for this. Give him some fine, sure.
Just so he knows you can't just kill someone and have no cost or consequences for it.
But he isn't really at fault here. This should be a legal decision someone can make.