The brain isn't fully developed until age 25. The evidence suggests that at least 70% of children who believe they are trans will identify as their birth gender after puberty.
I think that, for the most part, we need to get away from "male" and "female" stereotypes. There's nothing wrong with a boy wanting to play with dolls and to feed or diaper his baby. There's nothing wrong with a girl wanting to play with tools or build things. My cousin is an architect. She's a woman. She's married to a man and she's currently pregnant with their first child. She's still very feminine. As my username suggests, I'm a nurse. I teach nursing. I have taught, worked with, and been taught by a number of wonderful men who are nurses and aides. The ones I knew or suspected were gay were vastly outnumbered by the ones I knew or suspected were straight. There are some areas of nursing that are particularly well-suited to having men working, such as psychiatric nursing, occupational health and safety, and emergency room nursing. One of the universities in our area had a really neat program for high school students once. The students were sex-segregated into classes for a week, but the girls were taught engineering and STEM subjects, and the boys were taught nursing and human ecology (this is a discipline that encompasses the physical and social environments in which humans live; many human ecologists work in areas such as supervision of textile manufacturing or with families, for example). The goal was to encourage students to consider pursuing "non-traditional" areas of continuing education.