Eyesight is probably the biggest problem that comes with age, along with decreased mobility. If you shoot a rifle, that means optical sights instead of iron sights. If you shoot a pistol or a shotgun, that's somewhat different. The question is what's the range that you intend to shoot them and under what conditions.
Shotguns are kept for defensive purposes and also for clay bird shooting or for hunting. For a defensive shotgun, the key is rapid, accurate targeting. There are various sights that can help out: (1) high visibility "iron" sights that employ colored optical fiber inserts -- "fire sights" or radioactive inserts (Trijicon); (2) a forearm with a built-in flashlight on pump shotguns; (3) a quick-reaction red dot or halographic sight; (4) a laser sight to illuminate the target you want to hit. Of these four, the "fire sights" and quick-reaction types are also useful for clay birds and hunting.
Scopes on shotguns are for slug guns (hunting) and should be of low power. Either a short or long eye relief low power scope (personal preference) should go on a slug gun. The reason is that the range of the slug gun is limited and the low power scope gives you the maximum field of view.
The colored optical fiber inserts on "fire sights" glow in just about all ambient light conditions (except total darkness). Sights like the Trijicon with radioactive inserts are usable under all light conditions.
Red dot and halographic sights are usable under all light conditions and depend upon batteries for their operation. These electronic sights have adjustable brightness controls so that the projected dot or reticle is visible in the brightest daylight or total darkness.
Laser sights are really target designators -- where the laser do is, that's what you hit -- and represent an intimidation factor along with improved sighting. Lasers are not a guarantee of accurate shot placement because the laser beam is broken-up and scattered by atmospherics like fog, rain, and smoke.
The shotgun forearm with a built-in flashlight operates like the laser for target designation and for illuminating the target area. It also can be used to blind the target's ability to shoot back effectively -- but remember, the white light works both ways -- and it also identifies you as the target.
Handgun sights are much the same as a shotgun: (1) high visibility "iron" sights; (2) laser sights; (3) red dot or halographic sights; and (4) scopes.
Scopes are impractical for most handguns due to their size and eye relief requirement.
Lasers -- like the Crimson Trace LaserGrips -- are a great sighting aid for handguns.
High visibility sights are a "must" for any handgun under nearly all conditions. There are many different kinds and types from various OEM and aftermarket manufacturers. Trijicon makes sights with radioactive inserts that glow in total darkness; fiber optic "fire sights" are almost as good; Millet white outline or other 3-dot fast reaction sights are good in reduced light or bright light conditions.
Size is the major consideration with red dot or halographic sights. Most are designed for long guns, but some like the Docter are very small and compact. The Docter replaces the rear sight on most handguns and is a halographic sight. That is, it electronically projects a reticle onto the hooded sight glass. Put the reticle on target and that's what you hit.
This is just an overview of the kinds of sights availble to us shooters as our eyesight ages. If you have specific needs and questions, that's another topic that needs more detailed discussion.