Sorry, I tend to use "guys" for all people, but 'old guys' only for aged ones built like me.
I think you have to define why you breed fish.
You can try to supply a store. I do that with bags of tetras for a young guy's store. We're out of the mainstream geographically and shipping is very expensive. A few nice fish sold cheaper than the chain store here can, with locally bred written on the tank is good for him. I get store credit. Some try to do these things to make money, and I wish them the best. Energy and space costs are hard to overcome.
twotank specialized in a rare fish which was very expensive, and sold that one species because he had a stellar reputation in the small circle of people who kept it. Niche breeding like that can give you nice pocket money.
I'm a generalist who breeds to learn about a lot of fish. Lots of tanks, lots of turnover around a few core species. I like colourful fish, but more and more I look at fish in stores and wonder how they work. That's become the main focus for me, though I've learned if I breed a wondrous grey fish, no one wants the young and then I have a problem of space.
As for sharing, I've always liked barter economies for hobbies. If I see a serious breeder, I'd rather pass them a fish they can't get than sell it to someone who simply has money to spend. Many times, five or ten years later, I've gotten a note saying the breeder who got my fish had found something I'd like and bred it, and would I want some? That's how I built my killie hobby. I didn't often ask for money, and I didn't often pay for incredible rarities. What goes around comes around, often enough to be a pleasure.
Another type of breeding I once fooled myself into thinking I was preparing myself for is conservation breeding. There, you set up and breed endangered or extinct in nature fish, because if we don't, no one will. I bred a lot of Goodeids at one time, and some endangered rainbows. For that, you need infrastructure and connections with like minded people. We're like fruit flies breeding blue whales in conservation breeding - these species are ancient and we're short lived in relative terms. Very few hobbyists are able to build the level of network we need there, for all our talk, and while it's worth a try, you need very organized genetic data, studbooks and exchanges. You need likeminded people not far away, and a constant influx of new volunteers who stick with it.
LInebreeding to create new forms comes and goes in popularity, but demands resources, lots of tanks and good record keeping. It lends itself to places where there are show circuits.
The hobby is changing. It's moving to Asia, which will bring cultural changes. Here, my old club had an average age well into the sixties at meetings, and was almost all male. My new club where I've moved is already twice as big, majority women and has an age around the early thirties. So different perspectives will build different things, and I can pass along whatever old fish culture things are deemed relevant by the young keepers. If you're looking to breed fish in retirement, you have to know what's around you in terms of a community to profit from your efforts.
