The "male-or-female sex" sense is attested in English from early 15c. As sex (n.) took on erotic qualities in 20c., gender came to be the usual English word for "sex of a human being," in which use it was at first regarded as colloquial or humorous. Later often in feminist writing with reference to social attributes as much as biological qualities

Gender denoting sex has been used since the 14th century. This idea that it only applies to traits or behaviors is an invention of this century, and only popularized in recent decades. This is a nutcase, commie changing of the definition of gender to fit their weird ideological notions.

This person is right that gender was always synonymous with sex, as it was literally used to denote this when the word sex became associated with the act of having sex, or sexual themes. The very few people who used it that way in the mid 1900s were quacks and weirdo feminist philosophers and fake academics. It wasn't even adopted by anyone else. It was literally just these individuals using it that way.

Also, ever notice how there are 2 genders that completely correlate with what sex you are? Not a coincidence. It's because there are 2 genders, and 2 sexes. And that's why all government forms have always had sex and gender interchangeable. And it's why when someone asks you your gender, you reply with male or female, and don't launch in to a diatribe about how gender is separate from sex. Because it isn't, and a bunch of lunatic fake academics are trying to will their insane definition in to fruition because it's integral to their weird ideological ideas.