As of February 2015, the average weight of a 19-year-old male in America is 152 pounds, while the average female weighs 126 pounds. However, once a person reaches adulthood, an ideal average weight is determined more by height and body type than by age.
The generally accepted indicator of ideal weight is the Body Mass Index. BMI is a measurement endorsed by the Centers for Disease Control and Prevention and other health organizations and uses a formula that account for height and weight to determine how much body fat a person likely has. The BMI scale then determines an ideal weight for a person's height.