This can be stated in active form. Alternate translation: "no one is to use a razor on his head" (See: [[rc://en/ta/man/translate/figs-activepassive]])
The word "separation" is an abstract noun that can be expressed as a verb. Here "separation" is an idiom that means "dedication." Alternate translation: "the days that he has separated himself to Yahweh" or "the days that he has dedicated himself to Yahweh" (See: [[rc://en/ta/man/translate/figs-abstractnouns]] and [[rc://en/ta/man/translate/figs-idiom]])