You can have different genitalia than your chromosomes would indicate. Is it that hard to believe that you could have a different brain structure as well? I do believe that permanent changes should only happen once the individual is in their mid 20s, but at the end of the day I don't want governments making decisions on what others can and cannot do to their own bodies. Trans (and LGBTQ) people have been documented in history since language was first written, but somehow when the science is more definitive on these matters people become more phobic to reality.