DM- Dive Mule as we refer to it. When I worked with an instructor, it was lump tanks, watch students, set up his gear, lump it to the water (he weighed 427 pounds, so you can imagine the lead needed....) All this, and I was offered free fills. I personally do plan on becoming an instructor, but I am already a music teacher, so obviously, I love to teach.
Nowdays, I work on a boat in NC. Being a DM teaches nothing about boat management, but it does put you through some skills you will need. Guided dives for new divers, looking over divers to see what skill levels they are- cards mean nothing IMHO. Diving off a perfectly good boat in 6 ft seas because you get to swim after someone that missed the lines. Helping sooth nerves for someone's first ocean dives. A lot of these are basic rescue skills, the pro rating is required for insurance purposes. As for the other fun things I get to do, that weren't taught in DM, helping a diver set up their gear or put them in a wetsuit because they are seasick. Climbing into the engine compartment because we are 30 miles to sea and lost a clamp on the port side engine. Insanely hanging off the wheelhouse with 150 pounds of gear on, anchor in one hand, and having my heart in my chest as I hear the "GO!!!!" to plunge 120 ft, hoping to find the wreck, find a good spot on it that we can hook, and then try to destress on the dive.....
What do I get for all this? Well, my fills are free, my boat rides are free, I get lunch, and a place to stay. Then, if I am lucky, I get tips. Its amazing though, people tip 15% for a bad dinner, and $20 for a 3 days of diving (not even 5%). Still, to me it is worth it, but, as it states you are 55, you might think about not working on a boat. That is not to be mean, as one of the best DMs I have know was 64. What it is though, is people's safe return to the boat on a bad day (pretty, flat, clear days rarely have that type of problem) may be dependent on your swimming 400 yds or more to catch a panicked diver, then helping to pull them back aboard to help with O2 or CPR or anything else. That can cause a lot of strain.
As for things like discover local diving, etc, that can be very rewarding. When I am playing at a quarry and see someone with 'the look of scary green water- I know it, I had on my first dive after OW)' , I truly enjoy talking to them, being part of their buddy team, whatever. But then, I only go to pay quarries for fun, usually with some other DMs. Any of the limited access ones are where I am looking for stuff for my own purposes. Sorry to go on so much, I just thought you might like to hear from a working DM.
-J