I do believe there is no set element for anyone. Though these "what element you are" things do help people start off in their first experiences of magic.
We are all capable of elemental magic.
But alas, to your point of view, if you believe so in whatever element you are, these "what element you are" flowcharts or ways of thinking cannot 100% be accurate, they are generalized, and such, I hope you understand that some descriptions may be a little different to others.
I do believe in a variation of this though, but this variation is not determined by the star sign, month of birth or date of birth. The variation I believe in is Light beings and Dark beings. I know there will be outrage or debates on this, but they do not concern me, they can believe whatever they want to be true, I do not care for them. Even so, if you are a light being, after you have mastered the light being's variations of a Dark being's ability/technique, you can then learn the dark being's method of the light being's ability. Vice versa, after a Dark being has mastered the dark being's variate method of an ability, they can learn the light being's method.
Both are not evil, the light and dark beings exist as balance.