My daughter has preferred male characters and traditionally "boy" things from around the age of 2.
From 4, she started showing a distaste towards anything stereotypically feminine - pink clothes, dresses, "girl toys", princesses etc. She has loved blue, toys from the "boy section", clothes from the "boy section", monsters and superheros.
Her best friends at school are boys. She refuses to wear the "girl" uniform, so won't wear skirts and dresses.
She has expressed wanting to be a boy because "boys are cool" at times, and recently has said she wants her hair cut short "like the boys".
This is stereotype/gender role based, but imagine how easy it would have been to just tell her that actually, she is a boy, and give her a new name.