Does applying argan oil to hair prevent hair from greying?

No.

Premature greying can sometimes be due to endocrine and auto immune disorders ,so regular checkups are advisable. Avoid smoking, repetitive exposure to heat , chemical treatments and the sun. The diet should include foods like eggs, salmon, vit a rich vegetables, and provide an adequate intake of Vit D and Vit B12. Also the role of stress and chronic inflammation seems to be significant .