Hey, there are some proportion and foreshortening problems...but hey you are only 13, so they're pretty good.
My advice to you is not to just learn from comic books, or copy and use them as your only reference material. The problem with this is a lot of those cats haven't had formal training and though sometimes it looks really good, but it's a matter of style over substance. The problem with copying or using them for reference is that the mistakes they make will become exaggerated when copied.
I would look up classic artists Leonardo, Michelangelo etc. Use pictures from magazines and draw the basic shapes (cylinders for legs/arms, boxes for hips torso and head) which will give a better sense of the way the body works turns and looks in a variety of different poses.