I was recently serving as line coach during a defensive pistol class when I noticed an older fellow shooting his 1911 improperly. The thumb of his shooting hand, which should have been resting on top of the thumb safety, was underneath the safety. When I called this to his attention and pointed out that, under recoil, his thumb could actually force the thumb safety to engage when he didn't want it to, he told me about his battle with arthritis. He simply could no longer get that thumb up on top of the safety.
Physical impairment may be the result of advancing age, injuries, disease or birth defects. It really doesn't matter because these folks need to be able to defend themselves as much as anyone else. In fact, they may have a greater need because their ability to just get away from trouble may be impeded.
It is sad when a person studies the gun magazines and finds a particular type of defense gun that really appeals to them, only to find that they can't operate it properly. They may also find that they can no longer operate the defense gun that they have relied upon for years. Instead of giving up, it may simply be time to find one that works.
It is important to keep in mind that there are a number of handgun action types that will give good service for personal defense. The double-action revolver, single-action auto, double-action/single-action auto, and striker-fired autos all function somewhat differently, and you should consider each of them when you're trying to find one that can be handled effectively in spite of physical impairment.
Frankly, I would caution folks not to rely on your friendly sales clerk at the local gun store. While this person may be well-meaning and willing to help, he or she also might just be trying to move some inventory.
A person dealing with physical issues needs help from the professionals. A good idea might be to check and see if there are any doctors who are members of your local gun club. Thankfully, there are many pistol-shooting doctors and most of them are more than happy to help someone solve their problems.
An even better source of good information is the professional shooting school. Gunsite, Thunder Ranch , Whittington U and the Sig Academy, to name a few, may not advertise it often, but they do a lot of work with physically impaired students. Since they are not in the business of selling a particular kind of pistol, and they often have quite a number of different guns available to loan to students, they can often mate the student to the proper handgun very successfully. Just because a person has physical challenges doesn't mean that he or she shouldn't get training. In fact, these folks need training more than ever.
The key is to just not give up. Get professional help, try different types of guns, and go with the one that works best for you. If you always carried a .44 Magnum revolver but now, due to health issues, all you can manage is a .22 auto, go with it. That's still way better than chunking rocks. We can't always dictate the cards that life deals us, but we can stay in the fight.