I have been training for 19 years. I am currently 35 and I started competing at the age of 25 (in bodybuilding because I had previously done powerlifting). I had my first client a year after I made my debut on the stage, but before I really started making money from it, 5 years passed and I was very active on the Internet, IG, YT, etc. . it takes time to build a brand and if you really create good competitors, customers will start coming after some time, but it takes years - now coaching is my only job (I also invest in real estate or the stock market but it's passive income so I don't treat it as a job) and I earn as much from this as CEOs of large companies in my country, but it took a long time.
I never did it for money, only out of pure passion and love for bodybuilding, and believe me when I say that if you do it with money in mind, nothing will come of it.