If a 21 year old is 5 feet tall how can he become more taller?

You are probably still growing at 16 so you have that going for you. Here are some more tips: * Don't do any really heavy weight training exercises until you've stopped growing as the growth plates at the ends of your bones may be adversely affected therefore affecting your growth. Also, there are spinal compression factors with some exercises. * Improve your posture. Good posture can add inches to someone's height if they start with poor posture. Alexander technique or yoga can help here. * Stretching and hanging exercises will be most effective in lengthening the spine. A healthy, supple spine with healthy discs and good posture is the key.