You don’t need a degree. Start finding people who need help and training them. It is good if you have an “in” with a particular team or sports club. I play college volleyball; when I was in high school I worked as an assistant coach of a younger team for the travel club I played for and from there went to doing some private skills lessons and I always incorporated short GPP/conditioning sessions at the beginning and end and over time there just got more demand for strength and conditioning work.
Now I am entering my junior year of college and work with 10 athletes “full time” as a strength & conditioning trainer (during the summer + advise them via e-mail or phone during the school year) and the skills stuff is done separately. Results have been good so word of mouth has spread and I have more kids interested to start next summer and now expanding outside of volleyball players; their brothers or sisters that play other sports or friends or whatever.
I have no certification of any kind (I plan to sit for my CSCS next year, just so I can have some letters after my name), self-taught but just rely on my results to speak for me.
Start small, you won’t be able to just jump into having 20 athletes going full-time with you. Most importantly, you have to be able to get results for people and YOURSELF. Parents see how I myself get bigger/stronger/faster/better every year so that helps give me credibility even though I am young.
If I looked like I barely trained myself, nobody would want me to train their kid. Other than that, keep it simple and just get good results and your athletes will spread word of mouth yourself. My best “advertiser” was a client last year; she put on about 8 pounds of muscle and lost fat and got much stronger and more athletic and went from not making all-conference her junior year to All-State her senior year (definitely not all my doing, she got better technically as a player)… and she bragged how she lifted all summer, got stronger, whatever and now I have 4 other players from her school training with me this summer.
Alright, kind of long rant there and not sure how much help I was. Bottom line: start small, get results and most importantly, YOU HAVE TO BE TRAINING FOR SOMETHING. If you are no longer a competitive athlete, you will lose credibility and most important lose understanding with your own athletes. Powerlifting, bodybuilding, triathalons, whatever, you have to be training yourself.
If there’s anything else I can help you with, let me know.