Whats the normal weight of a 11 year old boy ?

Height: How tall is he? Without the height tough to answer. I would say that if he is of average height for his age say 4ft10in- 5 ft then 100-110 pounds is in the range. You must also take into account how active he is;video games vs getting outside and running around to develop muscles and ligaments (muscle weighs heavy). Does he eat a lot of junk food or is his diet good?

Normal Weight: Please see these growth charts provided by the Centers for Disease Control and Prevention. https://www.cdc.gov/growthcharts/clinical_charts.htm