Early greying of hair could be because of deficiency of Vitamin B 12 , it can also be influenced by stress. Prolonged periods of stress and anxiety , over a period of time, result in greying of hair . Malnutrition,  tension and other similar conditions may also slow down the production of melanin resulting in grey hair. Severe illness too can stop or affect the production of melanin of the hair. According to ayurveda Pitta (Fire) aggravation leads to grey hair . 

You can apply a hair mask once a week –   Soak Tea leaves(1/2 cup)  , Amla powder(1/2 cup)   and  1 tsp Eucalyptus Oil in an Iron pot overnight in water .In the morning add yogurt (2 tablespoon)  and 1 egg . Your hair mask is ready to apply . Leave it on your hair for 30-45 min and wash your hair with lukewarm water . 

In diet include  4 almonds , 1 Walnut and 1 fig (soaked ) daily, add Amla fruit in vegetable juice or chutney, take 2-3 servings of fresh fruits and vegetable daily.Do a light massage on the scalp with “Mahabhringraj oil” (baidyanath) twice in  a week.Avoid Pitta aggravating food like too much of spices , sour food and oily or fried food. 

For Vitamin B12- include seafood, eggs, and meats are good sources of vitamin B-12.