This is certainly a thing, but sometimes I wonder if it's a little more complicated. A lot of tradespeople do a very poor job of taking care of themselves. Poor nutrition, bad sleep habits, alcohol, smoking, etc. I think if you are going to rely on your body for your living, you had better keep up with the maintenance. It's also easy to just flat work too much, and while this is sometimes necessary short term, if it continues long term seems like it has a negative effect. I don't know your friends, however, and maybe they blow my idea out of the water.
It's also true that many retirement age white collar folk aren't exactly pictures of health either, though often for different reasons.
This thread has made me realize a lot of you, both trades and college educated, make way more money than me..........