Self-defense and use of deadly force laws are complex and open to a lot of interpretation by a jury or judge.
Usually, there must be a determination that if you have a firearm, that the attacker could inflict deadly force and you were afraid for your life. Yes, the guy was 77, but how would the guy with the tire iron be portrayed to the jury? Was the 77 year old a “gun nut” who loads his own ammo, practices regularly shoot at “human-style” paper targets and was spoiling to kill someone? An evil prosecutor can imply a lot of things.
Then in most jurisdictions there is the question of what would a “reasonable man” have done in the same situation. Unfortunately in liberal areas, a “reasonable man” might be required to call the police (even if they have long response times) and retreat.
In the concealed carry courses I have had, if you need to use your personal concealed carry weapon, you should plan on going to jail, have the contact information for a good attorney familiar with local gun laws in your wallet, and be certain, that your life (or someone you care about’s life was in immediate danger.)
How about 3 suspects show up to the old mans home in a stolen vehicle, they enter his property, one is armed with a tire iron, one is armed with at least a replica firearm....And no doubt these 3 all have prior convictions/criminal records.
How would you portray these suspects if you were defending them?