Comment by scotty79

I'm not quite convinced. Acting out on your non-heterosexual orientation or dressing up as opposite biological sex is also not immutable. You may act straight, and dress accordingly to your biological sex. Dressing as opposite sex is even similarly as rare as gender gaps.

And yet discrimination against people that display those voluntary behaviors would also be strongly frowned upon.

I don't think it's due to some innate nature of gender gaps. It's pure prejudice. "We don't like people like that because we believe people like that are less moral than us."

Maybe the time will come where ageism will raise to the same status as transphobia, but currently as you notice it's far from it.