I am 48 and have the same problem. I have found 2 things that help. When I hunt in a tree I only hunt the first or last 2 hours of prime time. All day hunts are sadly gone forever. I can tolerate 2 hours of pain for a chance of being a hero. Also if you hunt the ground you can move around from time to time to loosen up more so than in a tree. I have also found that hunting the ground is not so bad. I can judge distance better on the ground than in a tree. Probably because I rarely practice from a tree. Anyway, hope this helps.
PS If you find a cure please let me know.