Considering your age, you have the possibility to have black hair again. You must take care of your diet first, stop junk food completely, along with sugary beverages, colas, soda, excess tea/coffee. Include Antioxidant-rich foods: Fresh fruits and vegetables, whole grains like oats, brown rice, barley, whole wheat, amla, green tea, olive oil, fish, flaxseeds etc. For Vitamin B12- include seafood, eggs, and meats are good sources of it. Massage your hair with coconut/ olive oil with curry leaves added to it. Practise yoga and pranayama daily