First of all, what is your definition for "successful" model? As the previous comment stated, some models may be discovered; which has credence, just like actresses/actors. A very famous actress, many decades ago, was discovered in a drugstore at the counter, sitting on a stool drinking a milk shake (as I shared with my niece). How innocent and simplistic is that?? But remember, there are career routes a bit more complicated, and costly, so be very careful and use discretion with situations that may be too good to be true.
My modeling experience, as an adult, was not formal/professional. I was asked to model in shows and for publications mostly, but it was never a career. I was photographed for various events; and interestingly, while doing some housecleaning last month, I discovered my model photo book/portfolio of pictures, resumes, etc. That is something you might want to coordinate, if you haven't already. It was at the suggestion of a friend forty-four years ago WHO WAS a professional model. She was in numerous TV commercials, car magazines, etc., and was contacted frequently for modeling assignments throughout the U.S. I believe she started in her late teens/early twenties.
I've known young children and teens who started with modeling agencies, or by submitting photos to department stores. Sometimes, it's who you know in the business. Most importantly, be very cautious with modeling agencies. They can "talk a good game" and have you investing lots of money with little reward. As my mother always said, "Use your head for something besides a hat rack."
Check your local newspaper because sometimes you will see volunteer opportunities to model for events that might open doors for you. It's always wise to have a "back-up plan," as I told my niece for acting. Another suggestion is to view the Occupational Outlook Handbook from the Bureau of Labor Statistics. As a schooI counselor, I always recommended it to my students for a career search. https://www.bls.gov/ooh/sales/models.htm
Good luck, Beatrice!! Maybe I'll see you in a commercial, or at a fashion show.