Hi AJC! Always nice to answer questions from young artists! This is one of those "it depends" answers, and, as such, they are sometimes hard to answer, but I'll give it a try.
It depends on where you are in your drawing skills. If you are naturally gifted in drawing and work really hard, I would say you should be competent enough by the end of high school to get into a good art school, where you could further improve your skills. Drawing the human form correctly and in proportion is a huge challenge. Becoming really good at drawing of any type takes time and effort, and there is no substitute for that. Keep on drawing and learning from others.
I'm hoping you are taking art in your high school? If you are, talk to your art teacher; you might want to do a side-by-side comparison of a professional character/concept drawing and one of your best. With your art teacher, you should be able to evaluate what you are doing right and what you need to improve on.
As an artist, I have always loved to draw, there is something about drawing that both challenges me and relaxes me. I draw still lifes, botanicals, and landscapes for paintings and prints. I'm now in my 60's, and I feel pretty confident in my drawing at this point, but it took a while. I did a lot of drawing in high school and in college, and when I look back on those artworks, they actually seem pretty good, but at the time, I was not happy with them at all. I think like all artists, I'm always looking to improve my art skills, even now. So, a lot is personal perception, and that this why it is important to have art teachers or other artists around you, who can give you feedback as you develop your skills.
Best wishes! I hope this helps.