Overcoming masturbation

i was topper in studies from my childhood. i was such a razor sharp that my lecturers used to shock at my intellectual skills. i got state rank in my +2. On entering b.tech, because of a bad company of a friend, i had come to know masturbation. since that time(age17) I've been masturbating. now I'm crossing 25. Even i realised at the age of 20 itself,, i couldn't stop it. clearly i can see the effects of it now. my brain is not as sharp as before. but still enthusiastic in studies .Please Guide me how to stop that habit so that I'll get back my past health. and i was fully disappointed by my past.