I will be 72 in another couple of weeks, and have worked solo for 18 years. I am still in good health, and do not have health issues as the OP speaks.
However, at some point, I too will have to "get out." I still work the business 50, 60, and as much as 70 hours in peak times. I works six days, never on Sunday. But, how to "get out?"
Frankly, I would never find an employee to turn over the workload. I can't imagine sending somebody out with my equipment, to properties that I have worked for years, many of them over 12 years. If I thought working the business in the field left me with problems, having an employee with my equipment, my customers, would give me a headache like I've never had before.
At this point, I think the only way out is "cold turkey," that is, a clean cut from the business. Yes, I would still fret and stew on how well another LCO is doing with those properties, but I also know that I could not do anything about it -- that being a good thing.
I've read lots of threads about transferring accounts to another LCO, selling the accounts, or whatever terms one would like to use. I know of only two LCOs that I would ever consider discussing a transfer/sale. Nobody else does work like they do, nobody else handles themselves with customers as they. In this case, I know the track record of these folks. An employee to do the field work, as some have suggested, has no track record. I could never live with myself if my customers ended up with a bad experience as a result of any transition.
Just my thoughts, ... sure that some will disagree.