Hello dear, Height of an individual is determined by Genetics, Environmental & Nutritional factors and Hormonal factors (most important the Growth Hormone secreted by pituitary gland in brain) An individual stops growing in height after the fusion of the Epiphyses (growth plates) of the long bones, which occurs by the age of 17-21 yrs in males. So...as your son belongs to the above mentioned age group, he may still have a chance of increasing his height. Make sure that he takes a healthy & balanced diet, exercises regularly & avoids stress. Protein rich diet like soya, groundnut, pulses, etc should be incorporated in his diet plan. One more thing...avoid use of any over the counter medication which claim to boost the growth hormone & increase height...it may be harmful. Wishing your son a Good Health. Take care.