well a natural caster isn't really defined as anything, you can cast a spell from you heart and soul. You give your energy and will intent and your spells, rituals will work, just have faith and belief in your self.
But i do believe that there are some people who just have a natural ability in able to cast spells, mainly it can come from family inherantice. They past it on to ltheir children they can learn magick and spirituality.
But like i said magick comes from the heart, always have postivie energy and belief and everything will work.