How much should a skinny 13 year old weight?

Different people weigh different things depending on the way they are built. I wouldn't say that there's a limit because everyone is unique. I would say that if your 13 you shouldn't worry about your weight so much end enjoy life and don't get obsessed with it. You maybe so skinny and eat loads, that's just your body, you can't help it. So if you think your too skinny or fat then just remember it's your body's mass! Be proud of your body! I would say though, if you are worrying too much I would speak to a doctor and see what they think. Just don't worry if you think your too skinny sooner or later when you grow up you'll put on meat to those bones.