It all comes down to the concept and imagination of the story. Sometimes, even if you don't fit the typical mold, a special event or encounter could turn you into a magical girl. But usually, there are some hidden criteria or challenges to overcome.
Well, it's really hard to say. Maybe it's possible if you have a pure heart and a strong will. Or it could be that you need to be chosen by some magical force. The possibilities vary depending on the story's imagination.
It depends on the specific setting and rules of the magical girl story. In some cases, there might be specific conditions or circumstances that allow it. But in others, it could be strictly limited.