I disagree. You are going through puberty now. Therefore now is the time to get in the mode of being more active, eating nutritiously (cut back on your junk foods) to take care of the inner you as well as the outter you, your appearance. It is not too early for you to go for a brisk walk a few times a week or ride a bike, etc. Those are my suggestions for you. Also, with adult supervision, adding some light weights should help with toneing your limbs more. Don't get me wrong. I am not suggesting that you began a rigorous plan of any sort or become so obsessed with appearance either.
***We all know that the habits we develope as children are usually the same bad habits that follow us through adulthood in many cases, especially where diet is concerned.