My s-in-l has family members and friends what claim gender differences. It's really strange to see.
I’m a millennial. I know a great many people who “identify” as something other than their actual gender.
Mostly females who dress like males (the sloppiest sort of male). Shaved heads, auto shop duds. They tend to be ambiguous about their orientation; most don’t claim to be lesbian and most don’t have partners as far as I can tell.
I also know several people who don’t give anyone much of a clue as to what sex they are. You really can’t tell.
Among the millennials this is simply not uncommon.
By the way, when you talk with these people you find that their gender isn’t the only point of confusion. They’re on grade school level intellectually, and I don’t mean the upper grades. :(