It depends on what kind of vocalist you hope to be. For classical and opera, I will let some other experts on this forum give their views. From a jazz, pop, folk and R&B perspective, you can gain a lot of experience and confidence by getting out and playing gigs in solo or small ensembles at open mikes and caberets. If your town doesn’t have such opportunities, then try to attend some summer music camps that will expose you to that type of performance opportunities. (Berklee 5-week, for example). If your high school has an a Capella group, get involved so you can learn and experience new songs and gain more performance experience. There is a lot to be said also for knowing how to schedules, setup, and tune your voice in different kinds of venues with different types of microphones and amps.
Regardless of age you should be pursuing private voice lessons with the best teacher you can afford. Proper voice technique and vocal health are paramount to any singer. Technique will be the base of any style, and good vocal health will get you through future auditions regardless of what is thrown at you.