13 year old friend wants weight lift. his doctor said that if he lifts heavy in the 1 to 6 range then he will stunt his growth. is this true?

I am not sure: what the 1 to 6 range means but heavy weight training at 13 could potentially injure joints at the growth plate which is responsible for lengthening of bones. If insistent on weight training it should be done under the direct supervision of a professional trainer experienced with training adolescents and the goal should be toning not bulking of muscles,

Depends on meaning: I encourage my patients to find physical activities that they can be engaged in for a lifetime. The idea of lifting weights can mean many things. The aap and certified trainer groups recommend no power lifting until the final stage of physical maturity which is when you reach your final height.Training in proper lifting under supervision of a certified trainer is fine.