Both men and women can be witches. Men are also called witches, not warlocks. The word warlock actually means "oath breaker" and dates back to the witch hunts: It was used to refer to those who betrayed other witches, and in the witching world it still has a bad connotation.
A person does not need a "gift" in order be a Wiccan witch, only training. The Wiccan Rede is the witch's law and code of ethics. It says (in part):
Bide the Wiccan Law ye must, In perfect love and perfect trust. These eight words the Wiccan Rede fulfill, An ye harm none do as ye will. And ever mind the Rule of Three, What ye send out comes back to thee. Follow this with mind and heart, And merry ye meet and merry ye part.
See Witches' Voice: The Wiccan Rede to read the full text.
What this means is that witches should not perform magick that would harm another person. And if they do, it will come back to them threefold. So, if a witch hexes someone, he or she will experience misfortune that is three times worse. This is a very important part of the Wiccan belief. The magick they perform is supposed to be for personal change only.