My father died last November. He was not a big firearm fan like me but he had to qualify with them for over 30 years while working for the Federal Prison System and we always had a pistol or two in the house for home defense.
I use him as an example because he was an older man and did not routinely practice shooting like most of us. He liked simplicity and ease of use. Over the years, the main gun in the house was a Smith & Wesson .38spcl service revolver. Later on, it was replaced with a Kahr MK9. The Kahr seemed to be a better choice because of the lack of recoil (semiauto and all steel) and the trigger was smooth and lighter but still plenty long, so an accidental discharge is not anymore likely than with the revolver.
That said, 84 years old is up there in age. I think you need to be sure he is physically and mentally capable of safely handling a firearm. (Also, you should look at his driving ability.) MOST people that age are lacking EITHER the physical or mental sharpness to drive a vehicle. If he does "limited driving" then his firearm use should be limited too. (e.g. Supervised by you or someone else.)
Sic Semper Tyrannis