I have thought about stock on and off for the past 30-40 years and decided that it would be another way to ruin a very nice hobby.
I just dabble with my digital photos now and again,...
Making any money requires much more than dabbling. First you have to figure out what sells - no point in producing images that no one will buy. What you are interested in doesn't matter at all. Then get model releases from everyone and everything in the photo or the market is much smaller. And of course you have to produce a large number of saleable images on a continuing basis or the agency will drop you. Unless you are dealing with an agency that doesn't pay anything.
If you are looking for another job, it can work. If you want to dabble, it won't.