I'm 13 years old , 5'5"-5'6" and about 9 stones, everyone tells me that I don't look overweight and that I am just imagining things, but still I weight more than most my peers..
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First, your age has nothing whatsoever to do with your weight.

You're probably taller than most of your peers as well, and your weight and height are absolutely related. And your weight is PERFECT for your height.

None of this is about comparing yourself to others. This is about one thing and one thing only and that's YOUR OWN HEALTH.