For a 13-year old, the question is not getting back into shape but getting into shape all together. It requires support and work from the whole family. So: family meal times, no snacking except on fruit and veg, no fatty food in the house and no eating in front of the TV. TV watching and videogames should also be limited to certain hours per day. The key is to find some form of excercise that the 13-year old enjoys so much that s/he will keep it up. The beginning will be rough if the child is in bad condition as you need to be fit to enjoy some physical excercise. Try family games and walks. Go cycling together, play tag and catch. Get the child active by involving him/her in dancing or martial arts or horse riding or tennis-- or anything that the child may like. If the child is just not interested, start with a walk each night. It will allow you and the child to chat too. Incorporate excercise and play into things you do. Even blasting music and dancing around is excercise-- it doesn't have to be boring, but can be a laugh. In short: A 13-year old is too young to get into shape by themselves. Lifestyle changes are usually needed also in the family. 13-year olds are very fragile, and their self-esteem easily hurt. It's better to start making small changes yourself, rather than criticising the child. Make sure that any excercise or activity will also build their self-esteem. If the child is quite unfit, an easy way of doing this is by involving him/her in an activity that also involves learning skills such as joining the scouts. Well honestly you may just be ahead in growing because when i was 13 i was 5'3 and weighed 107 pounds. Look at the other people around your age tehy are probably shorter then you and you have probably just hit your growth spirt. If your are overweight just change your diet. Don't be like the typical teens today and go anarexic just have a normal meal and stop eating once your not hungry any more. Its a great way to stay healthy !