At what age did you realize you were trans?

Do you think age is important to know if you are trans? I ask because two days ago I spoke with my mother and she started telling me a lot of things about my "issue" (being a trans boy) and she told me that I never showed at an early age that I liked boy things and how she works with children. and she has seen boys playing with girl things, she believes them to be trans but not me, just because it changes from one day to the next (according to her). That day it broke my heart because he told me "YOU ARE NOT A BOY" and it's kind of sad because he was accepting me and him telling me that already makes me doubt a lot :(