A 17 year-old might grow taller if he grew some the past year, and his growth plates have not fused.
The pediatrician's growth chart for him can tell if growth has stopped. To look taller, one can choose properly designed clothing and shoes, and have good posture. Vitamins, supplements, "special" foods, exercise, etc... will not make a person living in the U.S. taller (height here is genetic).
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