A new study says men can get away with it as long as they don't have the additional responsibilities of managing a household. This is where it seems to work against women according to this study though I wonder if applies to women teaching tennis as well. I somehow don't think so.
One thing about the study that I found quite relevant was the point that arthritis was common among men who put in long hours but they tended to have fewer of the other degenerative diseases.
Meanwhile, women were subject to home stresses added to long work hours that seemed to set them up for many more health problems later in life. This points to the idea of balancing work, family, and recreation. Fortunately, tennis doesn't fall into the category of most corporate jobs that can be loaded with stress. I never felt the stress of hours on the court. If anything it was a relief from the management efforts of running a club.
The point here is that productive work can be okay and even long hours properly spent with time for rest and relaxation can be a good trade off.
Relative to the life of a tennis teacher or some other type of job that is more likely to fulfill personal goals you can see less burn out and greater satisfaction. I found this to be true no matter how many hours I put in on the court.
Having tennis as a career can allow you to combine all of these things with your avocation if your spouse is part of this. Another component that can make it part of a great lifestyle is to have your kids involved. Tennis as a family affair seems like the ultimate example of work, play, and family.
The Everett family comes to mind along with some teaching pros I've known where both spouses worked as teaching pros and their kids became active in the sport eventually getting a free ride to college on scholarship and making it a career as well.
Long days on the court can be a way of life for a tennis pro, but in addition to the satisfaction of helping lots of players you may find that it helps you as well. But for the arthritis, I can say I don't regret any hours I spent on the court whether teaching and coaching, or playing. I earned enough money to pay my bills and with some discipline and delayed gratification set up a safe and reasonably comfortable retirement. And remember, for me teaching tennis was a form of retirement from the hazards of jobs that left you worn out but uninspired no matter how much the pay.
Additionally, tennis gives you the option of doing a slow fade into retirement where you scale back your teaching hours as your energy levels flag and your physical abilities drop off. Stamina is the one thing I found that you lose over time no matter what you do but at least as a tennis teacher and coach you can dial it back as needed.