White hairs popping up at the age of 33.

Hello doctor My age is 33 and I maintain a good physique as I'm into weightlifting and martial arts for 10 years. Once I crossed the age of 30. There was hardly 1 or 2 white hairs that visible. Now, within 3 years of time, almost 10% of my total head hairs have turned white. I'm terribly shocked and upset as I'm unable to find out the root cause of this. And worried how I would look at the age of 40. I know getting white hairs is inevitable as all humans will get it once they cross the age of 50 or 60. But why did I started getting it at the age of 30??? Is there any treatment to make it black again. This affects my self confidence level which eventually leads to stress and depression. Pls provide ur valuable suggestions