Haha, I'm right there with you on the young artist thing(I'm a mere 13 myself). Anyways, this is a stunning style. The prominence of the bone and muscle makes for a style that resembles a real horse which I am very fond of. The ears are very cute and expressive, so a round of applause for that. The eyes are a good size and shape and I love that large, stylized tear duct. Those eyebrows remind me of Spirit, and can help give your character a lot of expression so another well done on that aspect. Now for the, err, not so positives... The highlights on her hair are a bit nonsensical. If you are going to make her mane shiny, keep in mind the direction of which the light is coming from. Here the shiny areas are place willy nilly, but with some work, they could be very effective in making the hair pop. The curls in the mane are a bit off. This bit would best be explained with some visual aids so hop on over to that spoiler to check it out.
I spend a lot of time around and riding horses and I have come to known their anatomy fairly well. That chest juts in weirdly, which would be a life-threatening characteristic on a real horse as it would leave no room for the heart and lungs. I hope this has helped you and I look forward to seeing more art from you! Stay Foxxy!