During my high school days, I was a pretty decent golfer (about a 2-3 handicap, for you other golfers out there). I was asked by my local club professional if I would help him teach his junior golf clinics that summer. If you have specialized skill in any sport, there are definitely opportunities out there for teaching others the fundamentals (and getting paid).
However, like anything else truly worthwhile, apps require a significant investment of your time or money upfront. If you don't have the skills, then you have to hire someone who can assist you in creating a great app. But first you need to come up with an idea that will sell. Do the proper market research and analytics to come up with the right app.
How much will you make? I think my best month with Google AdSense was almost $5,000 over the last ten years. That amazing month blew my mind since it was actually near the beginning of my blogging journey. When you go from making zero to $5,000 in a month, that will rock your world. For me, it also got me even more excited because I knew there were other ways to monetize.