Hi, friend.
There are number of reasons associated with early Graying of hairs. Heredity, stress, tension etc. are some of the reasons behind it. Start applying henna once in a week.
You can try another home remedy. Burn some amla in an iron vessel until it turns into ashes. Put down to cool and then grind finely. Now mix this with your hair oil. Massage with this mixture at least twice a week followed by a hot towel wrap.
GOOD LUCK!
Abigail.