The average weight for a 13 year old boy that height should be around 46.3 kilograms or 102 pounds although it can vary from 85 to 135 pounds.
How much should a 13 and a half year old boy weigh if he is 160 cm?
I'm 13 and I'm about 5'2" (160 cm) and I weigh 90 lbs. I think I'm still inside the "normal weight" zone but probably on the lower end.