As a "ancient old guy" - the only thing I can say to a young buck of 43 is that by now, you ought to be able to point that long rifle and hit what you're pointing by instinct! LOL
All kidding aside - it happens to everybody. I know our ancestors had the same issues based on original rifles I did work on years ago as well as original barrels I have owned. When a shooter's eyes began to give them issues, it was a common practice to move the rear sight further towards the muzzle. Might sound strange, but it was done. I built a flint Virginia style long rifle about 40 years ago and shortly after I finished the rifle, I noticed I was having eye/sight issues. I was down at Friendship talking with a friend who used to have a booth there - he had made the hand forget furniture for the Virginia style rifle I had made. He showed me an original Bean rifle that had had the war sight moved forward four times. A new dovetail had been hand cut each time and the old dovetail filled.
Long story short, we removed the rear sight from my rifle and he helped me try different positions bt taping the rear sight to the barrel with some tape he had until we found the position that allowed me to get the clearest sight picture. Once we found it, we marked it and he and I cut a new dovetail with tools he had. Once we got the rear sight installed in the new position, I went over to the line and bought a practice target and was amazed at the improvement. I filled the old dovetail once I got back home in Michigan - I ended up moving the rear sight two more times over a period of time.
As silly as it sounds, you might remove your rear sight and with some tape - reposition it and see if it gives any improvement in clearing up your sight picture. If not, easy enough to put the sight back where it is now and all you are out is a little time. Then you can go to a good eye doctor, get a good thorough exam - explain the issues you are having and see what they suggest.
Good luck - and you're not getting old - it's like good cheese and wine - you improve with age!