I have a son 16 years old and he is having hairfall from now. i can even see some part of his top head from a height?

Depends on cause...: Hair loss at 16 years is too early. One's primary care doctor can check for medical causes. If none are found, then one can see a dermatologist, especially one specializing in hair. Medical causes may include: hormonal problems (low thyroid), seborrhea, alopecia areata, stressful illness. Other causes: genetic male/female pattern baldness, telogen effluvium.