Hair Turned grey. On beard as well?

Hello..! I am 28 years old and at least 40% of my hair turned grey, when I was 24... my hair started to turning grey...I saw there is a bunch of grey hair about 50-60 hairs altogether at one place in front, makes me feel in-secured. Many friends of mine also have grey hairs and I saw that they are using dye to cover their grey hair. So, I started using the same to cover my grey hair. After using dye, the frequency of grey hair is got increased and I stopped using dye to cover my grey hair it's been more than 6 months and I have not used any colour. Now, my 40% - 50% (approx) hair turned Grey and now my beard is also started to turning grey. Can anyone please tell me is it possible to reverse the grey hair ??? If not, is there any possible solution, to stop the remaining black hair from turning grey. Also I bought kerablak serum today, is it helpful ? Or can I use that serum on beard as well ?? Please suggest