Yes love peep sights but that's where my problem started on the Winchester Model 94. I could see the target clearly through the Williams peep but the front blade was a blur. Add the glasses, sight through the bottom lens of the bifocals and the front blade is clear but the target is a blur. A no win deal so traded for a Marlin and a scope. However, the longer sight radius on most traditional muzzle loaders I now discover overcomes the problem even with a 28" barrel. The rear sight doesn't seem to be an issue but if it becomes one I'll add the peep sight.
With open sights, you will never be able to get the rear sight, front sight and target in focus at the same time. It has nothing to do with your age, physically, the eyes can not do it.
With an aperture sight, the smaller the aperture the longer the depth of field, so with a small enough aperture the front sight and target can be in focus but they will both be dark.
For target work, I use a smaller aperture but that is under controlled conditions.
For hunting, I unscrew the aperture and just use what's left.
Then it is back to basics, focus on the front sight, line up on the target, breathe...
Good luck
Oh, I did find a neat aperture sight for muzzleloaders, on an original Ohio rifle. Just a bent piece of iron with a hole in it! Anchored to the barrel and extending over the wrist. It also had a long screw through the piece that sat in a dimple in the tang to allow for elevation.
Haven't put one on the 1803 yet, but I might.