I'm going on 53 and plan to start a DM program this summer. I don't see it as a new career, mainly because there's no real money involved other than an occasional tip. I would only work as a DM in my local area, not overseas where I will just want to be on vacation. However, I do hope being a DM will help support my diving habit, and allow me to deduct some of my diving expenses for tax purposes.
The tax implications/benefits have been discussed on other threads here over time, try a search. The upshot recommendation is that you oughta talk to your tax accountant before heading down the road if tax deduction is part of your decision making rationale.