I would add that while aging is a factor, a lot of it involves disabilities of one sort or another that may not correspond with physical age.
Often, revolvers are mentioned as a possibility for self defense for the elderly--easy to check if loaded, easy to load absent time pressure, uses a variety of ammunition including low recoil ammo, and a simple manual of arms. But the downsides are : firing DA is difficult with less hand and trigger figure strength, recoil can be accentuated, reloading can be difficult under pressure due to mechanical manipulations required, limited ammo capacity, in steel--they tend to be heavy, and dropping them can damage them requiring a gunsmith to repair. The single action capability goes both ways--it greatly lessens the trigger pull needed to fire but it requires dexterity to decock a revolver safely. Single action can also be a problem with those lacking sufficient feeling in fingers due to neuropathy whereas accidental discharge likelihood may increase. It is a similar issue with a larger heavier revolver has less recoil and may be easier to handle but it is obviously much less concealable if outside of one's home or car.
Semi-automatics pistols are the other main possibility. The advantages are capacity, recoil handling as part of the recoil impulse is directed into the operation and the impulse itself can be less abrupt due to springs, etc. that stretch it out, usually cheaper than a quality revolver, easier to reload with magazines, usually greater capacity than revolvers, and allows a safety of some sort to be employed (grip, trigger, and/or manual safety). Modern semi-automatics also allow sizing the firearm to the hand a bit more than changing revolver grips so that the power crease between the first joint of the trigger finger can be employed which increases leverage and trigger control. In addition, the 1911 and Browning Hi Power pistols are famous for suiting a variety of hand sizes with tinkering with grips or the flat/arched mainspring cover/housing of the 1911. These also come in an array of different sizes, designs, makers, etc. and pretty much every reputable semi-automatic is tough enough to keep firing if dropped. Most modern ones are drop safe as well.
Disadvantages start with the more difficult manual of arms, some designs, particular striker types, can have very tough recoil springs in order to charge the firearm, this can necessitate using a alternative that can be a bit less safe to rack the slide, malfunction drills can be difficult for those with little hand strength and dexterity, etc. Hammer fired often can ease racking the slide if the hammer is cocked (which might increase risk of AD depending on the model) but usually have a heavier trigger pull. Hammer bite can also be an issue with some with the high hold and accidentally hitting the controls such as a slide release, mag drop, or safety can be an issue.
Visual acuity can be an issue for both semi-autos and revolvers and can be ameliorated to some degree by tailoring the sights to the firearm but this is best done when acquiring one or after familiarity with a particular firearm. That way, the sights are either part of learning the firearm, or simply adjusting the knowledge of an existing firearm to firing with new sights.
I would suspect that the problem of disability and aging is most acute with those who have little, if no firearm experience, and are not familiar with any firearm type. There, the role of the trainer and sales person is critical. Just like the persistent idea of little guns for the women, you get a salesperson or trainer focusing on selling or teaching what works for them and not the customer. Recommending heavy service firearms that have to use belt holsters might not be the best for someone with back issues, they may lack the dexterity to use an IWB, and so on. In the home, many folks might also have problems fumbling with firearm controls in the dark and that medications etc. that can affect the nervous system are often prescribed to be taken at night. Arthritis and joint stiffening can also occur which is often worse when the joints are at rest for awhile.
I think also that we cannot overlook that long arms, either rifles or shotguns, can also be easier to manipulate and easier to fire in some conditions. Modern hi-tech sighting systems and lights are also a common accessory and most people can be taught to shoot long arms far quicker and more accurately than handguns--this is especially true for those with disabilities.
There are some caveats though, while a 12 gauge shotgun might be a closer in a fight--it is also a bruiser unless you use the mini-shells and/or a gas gun or recoil reducing stock. However, a 20 gauge shotgun shell has the approximate energy of two .44 Magnum shells going off at the same time and is available in gas guns along with recoil reducing stocks. However, things that can work for ordinary folks like pump action may not be appropriate for those with limited hand strength as short stroking a pump can render it useless in a fight.
In addition, modern black rifles like the AR system chambered in 5.56/.223/7.62x39/.300 Blackout are also ergonomically friendly, have much less recoil than a shotgun, pack a wallop, and at least in the 5.56/.223 can penetrate less through walls than some pistol ammunition. These can often be quite light if not loaded down with useless trinkets but without the commensurate increase in recoil. Sight lines are longer as well and most of the controls do not require much in hand strength to operate. Ammo capacity in these cases exceeds what was probably fired in total by all parties at the OK Corral in just one magaine but these are exceedingly easy to reload in the AR or AK platforms. An AK or SKS can also serve but some of the controls are simply not as ergonomic as the AR despite my liking for both systems and weight can be an issue with the fixed mag in the SKS. I know a lot of folks also like the older pistol caliber carbines or the M1 Carbine in a home defense role as well which have the advantage of possibly lower flash and noise. A lever action cuts both ways as it does require the dexterity to operate a lever but if familiar to someone can be operated pretty fast and in some potent self defense calibers--the pistol caliber lever actions are particular worthwhile to consider.
I would venture to guess that many of the old line trainers might actually have changed their teaching to accommodate students with disabilities or aging related issues. Not so sure about others but it might be interesting if some folks actually started considering these factors at places like the NTI and other trainer forums as the American population is rapidly aging with a similar increase in disabilities.
Thanks O/P for bringing this up, I have been thinking about these issues for awhile due to personal familiarity with the subject of your post. Sorry to others for a long post.
