l'oiseau,
How old is your Fox paddle? I am assuming it is a FoxWorx, either bent shaft or straight...All of their new paddles have epoxy resin coated shafts...should be easy enough to add some reinforcement (glass, even wrapped twine) and saturate with epoxy resin. You can get quality epoxy for decent prices at RAKA...
Now, for your shoulder...some of the corrective strokes put odd stresses on your joint. For nearly every stroke, there is an alternate stroke on the other side that can accomplish the same (or nearly) corrections with less stress on those "aged" joints.
For example, rather than that pry on your right, try a draw on your left...Especially since your objective is enjoyment of the paddling and scenery, a less efficient set of strokes shouldn't bother your progress, as you said, you're not racing.
And lastly, for the physiology aspect. We all have some control over how we age. Granted, genetics and accidents/injuries have influence, but a balanced diet, sensible blend of aerobic and weight bearing exercises can go a long way to maintaining a healthy, active lifestyle. Sure, age is a factor, mostly related to length of recovery to injury.
I always say, most people spend the first half or their lives ignoring their health, and the second half being reminded of it...Not to say that describes you in particular, but the days do have a way of sneaking into years!
For me, at 57 years old, I am pleased to be able to mostly keep up with my kids, my nephews and their friends. I still bike about 2,000 miles per season, it's a fantastic way to manage stress and stay in good cardiovascular shape. Some weight training, and then a wide variety of physical activities keeps me young, or at least deceives me into thinking I am!! I used to wrestle, and I was an amateur boxer...I had reconstructive surgery on my shoulder due to recurring dislocations (more than 30 times, I lost count) and I was in a horrific bicycle accident. All of these things took their toll, I'll never be the man or athlete that I once was...but that's OK.
As long as I can still get out and enjoy myself, it's enough.