The moment this question came up, I knew that this was a good question for MDC. You folks are diverse enough in your thinking and your life experiences, and kid-centered enough, to respond to my question in a thoughtful way.
My son, now in fifth grade, decided last year that he wanted to grow his hair, to be like his best friend and many of the other boys in his elementary school. He has succeeded in growing his wavy light brown hair to his shoulders. It is extremely pretty hair! It has blond and red highlights, it waves around his face and forms curls at the bottom.
It's just long enough for a ponytail now if we form the tail high on his head, but that makes him look like he's wearing the hairstyles that were popular for little girls when I was one. (Little ringlets come out around his face.) He doesn't like to wear it pulled back because it doesn't all fit into the ponytail evenly.
My parents think he looks like a girl. He has always had a very sweet face--long eyelashes, large eyes, and so on. I think probably a lot of people misgender him. He's not a super athletic boy, but he likes computer games and fart jokes and chess and superhero comics and physics and water balloons, so all his friends are other boys and I never have the sense that he's secretly a girl. (Not that a girl can't like fart jokes and physics, of course.)
My parents started to give me a hard time about his passport photo. They are worried that if his long hair isn't somehow pulled back or hidden, he will be misgendered in the airport. Not that they used that word, of course.
So! Do you have a boy with long hair? Have you ever taken a trip requiring a passport with a boy with long hair? Has your boy with long hair later regretted ever having had long hair? I am entertaining my parents' issue seriously. Is this really a problem? Do I need to find a way to clip my son's hair back for his passport that makes him look more butch? I really don't want to make him cut his hair.