Weight and Age are independent of each other unless you are talking about little kids even then, because of height and genetics some are bigger than others. What you are looking for is making sure that one's weight is right for their height and the best way is BMI calculation (Body Mass Index) check out Health Central's Ideal Body Weight Calculator here http://www.healthcentral.com/diet-exercise/ideal-body-weight-3146-143.html
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Kenn Kihiu
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