According to the Centers for Disease Control and Prevention's growth charts, the average weight for a 13-year-old boy is around 100 pounds. This figure is the 50th percentile for a 13-year-old boy's weight, but there is a wide range of normal weights. How much a teenager weighs will be influenced by genetic and environmental factors.
There is a formula that may be useful in predicting the final height of a child based on the heights of both parents, but there are often exceptions, and it is considered more of a guideline than a hard and fast rule. Add 5 inches to the mother's height, and the result is added to the father's height in inches before being divided by 2 or (mother's height + 5 inches) + father's height divided by two.