Not quite your age... But starting to realize the long term toll on the body from the trade, mostly back and knee issues. (Many of my posts here are from when I too can't sleep late at night.) But have noticed some slight "carpal tunnel", and general arthritis issues. Outside of being something for your doctor to advise you on, I have found that just changing some work habits helps out a lot.
Reduced wieght tools, switched from Klien to Knipex, and Witte for all hand tools.
Got a wire nut driver for my lighter 14.4v (thought of moving to 12v) screw guns and impact wrenches.
Threw the tool belt/bags away!
Wear Skillers pants with a small pouch, and built-in knee pads.
Work smart... Organize work for efficiancy and minimal effort.
Start moving towards 'directing' more work towards young and eager guys, than you actually physically do!
Think about what the causes of the pain in your thumbs are... If it's from something you do a lot of. Like cranking screws, or cutting wire, etc. Think about how you can change how you do it. A slight change in a habit, could make you feel better.
