I'd visit an ophthalmologist just to rule out something serious but unlikely like glaucoma. That said, presbyopia is the hands down most likely thing. I think almost everyone gets it eventually.
I'm not sure what kind of shooting you're talking about. For e.g. Bullseye AKA Precision Pistol, people just use red dots, usually the tube type like ultradots. They work every bit as well as iron sights, and the geezers can stay competitive until, eventually, their hands get shaky. That's usually looong after the eyes go. I expect hunting would work the same.
For defensive type shooting, I dunno. The micro red dots solve the presbyopia problem, but come with their own problems. Different sights might help, e.g. I found that XS Big Dots helped over conventional irons, but unfortunately it keeps getting worse; now I can't really see them very well either :-(. But it's worth trying some different ones - fiber optics help some in bright light (and in low light Lasergrips etc work well, with the usual caveats).
The bottom line is that I now put dots or scopes on all my rifles, and my defensive pistol accuracy just isn't as good as it once was. If it's any consolation, if you have the other basics - grip, trigger control, ... -down, you can still probably shoot a lot better than most folks even when the sights are fuzzy.
And to answer the question you actually asked :-), I don't think there are any exercises or whatever you can do, alas.