The cause of white hair can be genetic, excessive exposure to sun or pollution, smoking, excessive alcohol intake.
diet deficient in protein, b12, iron, folic acid,zinc and selenium,
excessive consumption of sugars, sweets, bakery, biscuits , cookies, cakes, pastry, junk, chocolates, ice cream, rice without dal or pulses or curd or nonveg.
Excessive amount of the above mentioned food leads to fast ageing which appears in whitening if hair.
Evaluate yourself and see what is causing whitening of hair