A childhood belief about belly buttons

I used to believe that only males were allowed to show their belly buttons as it seemed whenever males had their shirts off it would be showing. However, girls back then hardly ever wore bikinis, never had their bellies showing, and when a girl did have a belly button showing it was a big deal. Even my female cousin used to say how lucky I was to be a boy because whenever we went swimming mine was always showing and she loved to look at it. She’d always complain how she wasn’t allowed to display hers. To further this belief, in gym we boys had to take our shirts off sometimes and had our belly buttons showing even in front of the girls, while the girls were always kept well covered in their gym outfits.