I decided to become a (volunteer [0]) firefighter at 60 (software development background). It has been awesome.
Last year, I considered becoming an "EMR" (Emergency Medical Responder) - the lowest level of certification for emergency medical care that there is (basically, you can get vitals and stats from the patient if they are conscious). Because of timing considerations, I ended up not doing the course.
A year later, I see my 2 fellow firefighters who did become EMR's having to 20+ hours a year of mandatory continuing ed/training to their lives, and I'm pretty glad I ended up not doing that.
The firefighter part, given that we're a small, very not-busy volunteer rural fire district with an awesome district chief and culture, continues to be fantastic.
[0] thanks to the unions in my county fire department, volunteers are required to go through all the same certifications as career firefighters. We lack their level of experience (mostly) because we don't go on as many calls.
I went the other way. Small town ambulance station was chronically short of people to keep the truck staffed, and I figured I could spend some time. Did a year of ride-alongs, took the EMR course on my own dime, and after licensing, joined for part-time on-call. It was convenient for me at the time, where I could stay at home near the hall for my shifts, and then go if paged. They did eventually move to 12-hour fully paid shifts, which is better for retaining paid medics, but less convenient for some like myself. Those 12-hour shifts at the office were certainly less fun though. Did that for ~ 6 years.
Moved three provinces over, and joined the volunteer fire department, doing FF and medical first responder calls. Back to just carrying a pager wherever I go, but otherwise largely back on my own time. If I'm available, great! If not, well, it's volunteer. It sure helped get acquainted with our new community, and met an awesome bunch of folks. It'll be 12 years for me in 2027.