@Norwegian Cave Diver I envy you...
Planning to work as DM after retirement implies 3 things:
1) being able to retire early
2) being in good health
3) being motivated to continue to work hard and to assume significant responsability.
I do not meet any of these criteria, as I will retire at 70, my health is already bad now at 63, and I decided that being a diving professional was too demanding for me when I ended my professional diving career, back in 1989, when I was 31.
However at that point I had been working for 5 years as DM and instructor in touristic resorts (in the Mediterranean and at Maldives, with a short period in Kenya), so I can provide my vision on this job.
First of all, I was working half time as a diving guide (in the morning) and as an instructor (in the afternoon).
These are two quite different jobs. The diving guide has to manage a group of expert divers, often driving the boat and managing the related nautical activities. The dives can be deep, in our organization the limit for recreational divers was 50 meters with deco. We did dive also in caverns and wrecks. The customers were often undisciplined and the DG had to be authoritative. I was young, many divers were twice older than me, and it was sometimes difficult to be obeyed.
Instead teaching was easier and less risky, there was some activity in the pool, some in the sea in a few meters, starting from the beach. Students were literally doing anything you asked them to do, I was like a god for them.
Working in exotic resorts is entirely different than working in a shop in a normal town. I have no direct experience of the latter, as it is something which did never appeal to me.
But there is a third possibility, which instead I did both before and after my years in the resorts: being an active instructor in a no-profit organisation, a diving club.
This is very stimulating, particularly if getting some wage is not your priority. Diving clubs are very nice social groups, where you find a lot of friends. All real friends in my life are fellow divers I met in that diving club. Some were the instructors who introduced me to diving, some were students who trained together with me, some were my own students.
If you plan to find a good activity for your retirement, evaluate joining or founding a diving club.
There you can teach, operate as a diving guide, be the organiser of travels and excursions, organise civil protection activity in cooperation with authorities, etc.
Many diving clubs are structured as no-profit charities, so instructors and DMs are classified as volunteers.
Of course, also a diving club is affiliated with some training agency. So you must qualify with the same agency for being able to teach in their organisation. So in this a club is very similar to a shop.
Of course usually clubs are not affiliated with for-profit agencies, such as Padi, as this would not cope with their not-profit statute.
Here in Europe most clubs are affiliated with not-profit organizations, such as Cmas, Bsac, Fipsas, Barakuda, etc...