Can premature graying be caused by a copper deficiency?

Reportedly yes. Graying of hair is related to genetic predisposition. Age of initial graying is largely a matter of genetics. However stressors: nutritional deficiencies, chemotherapy, traumatic head injuries, low vitamin B levels, zinc deficiency, severe illness, surgery & marked emotional stress may impact earlier depigmentation in people who are already predisposed to gray hair. Aging is a significant factor.
Rapid turnover. The loss of pigment in hair comes from too rapid turn over of hair shafts from the follicles. No great cures have been proven to work. Some people think that taking biotin can help.