First of all, I am like you... I didn't start experiencing any gender dysphoria at all until about the age of 13/14.
And I think it might help you to know, WPATH acknowledges that it's completely normal for people to not know that they had gender dysphoria until that age. I'm going to copy the next two paragraphs DIRECTLY from the WPATH standards of care so that you can see it for yourself.
"In most children, gender dysphoria will disappear before, or early in, puberty. However, in some children these feelings will intensify and body aversion will develop or increase as they become adolescents and their secondary sex characteristics develop."
"Many adolescents and adults presenting with gender dysphoria do not report a history of childhood gender-nonconforming behaviors. Therefore, it may come as a surprise to others (parents, other family members, friends, and community members) when a youth's gender dysphoria first becomes evident in adolescence."
Basically, this means two things...
1. It's not childhood gender-nonconformity that's considered the hallmark of being trans. It's aversion to the body's secondary sexual characteristics.
2. WPATH acknowledges that sometimes dysphoria doesn't develop until adolescence, until that period where the body begins to go through puberty and thus sexually-differentiate to a form that's against the mind's programming.