I recently told Hirakoba-san that he shouldn't cut his hair. I think if you're happy with growing it out or keeping it at its current length then you shouldn't listen to your mom. Perhaps she thinks putting it up like that makes you look too different and she doesn't like that, but plenty of men with longer hair have been putting it up into ponytails and "man buns" though I heard the latter can cause hair loss, so I don't recommend doing up dos tightly if you'd like to keep your hair.