I am in fitness as a trainer and group exercise instructor part-time (approx. 20 hours per week) as I have two young children. However, I treat it as a career and my passion shows.
My schedule is full and I retain most of my clients, and if I could do this full time I would.
I absolutely love helping others to lead a fit and healthy lifestyle.
I think it is possible to do this part-time if you have a passion for it. There is absolutely room in this industry for instructors and trainers to give their limited time and do it well.
Good luck to you!