I think you're pretty good as an artist, especially for your age. However, and I know many people say this, try to draw realistic before doing cartoonish. If you have a cartoonish style for too long, it may be a hard habit to break. This is from reading another cartoonist's experience, not my own. Here's the cartoon he used to portray his feelings.
http://fav.me/d37650v I highly recommend you read the deion, it inspired me. xD