How to cure premature grey hair.

Dear Doctor,

I've been having grey hair from the age of 16. Now I am 29 years old. Most of my hair is grey now. How can I get my original black color back. This is a problem to me. I have seen in so many web-sites saying that B-12 deficiency, a thyroid imbalance, anemia, along with many other conditions would cause premature graying. Is this true? If so how can I solve this problem without dying my hair. Is there any medication that I can use to cure this problem.  If I am 40 years this wouldn't be the case. I will be ok with it. But I am still 29 years old and not married yet. Please can you give me advice to cure my grey hair problem. I heard that there is so many medication to cure melanin deficiency. e.g. melatonin tablets. If so can you please tell me what type of tablets would be best for me. Now I have gray hair on beard as well. Please help me on this.

Yours,

Imran