Outside of traditions of witchcraft, which may have their own rules, and criteria that need to be met, the way in which you, become a witch is simply by practicing the practice of witchcraft. Much like how a guitarist, becomes a guitarist by playing the guitar. You do not need to reach some form of level, and you do not need initiation. The title becomes available to you as soon as you begin to practice, you can choose to not identify with such a label, if you do not want to, but you definitely fit into the descriptive use of the word, and could still be referred to as one. So in order to become a witch start studying, and practicing witchcraft in whatever form calls to you, if nothing is particularly calling you start reading any books, and articles, watching videos on the subject, and/or finding witches to communicate with. Take the information that you gather, and use it to start your practice.