multiple factors can cause early greying of hairs. Iron deficiency, VitaminB12 deficiency, Calcium pantothenate deficiency, others like positive family history, Atopic individuals like in your condition can have early canities . Please do visit your local dermatologist and get evaluated and treated accordingly. In most of the cases, greyed hairs cannot be reverted to normal black hairs, but further greying can be arrested at proper intervention.

have plenty of leafy vegetables, fruits, calcium and B12 rich foods etc