This reminds me of the condition I was in 10 years ago. Slaving for a landscape supplier...loading boulders, pond kits, etc. for landscapers and homeowners....I completely TWEEKED my back. The manager did not believe me, even though I was hunched over when I walked. This is when I made a strong push to get my own thing started.
Well, not to take up this whole entire page with the long version.....Here I am TEN years later....yes there are aches and pains...The older you get the more stretching you should be doing. Yes I am in great work shape, but we know how physical simply mowing lawns can be.
I live by a motto I stole from a guy "Work Hard, Take A Break".....along with "Work Smarter, Not Harder".
Once you are in a position...DELEGATE work.