@Cousin_Isobel I get lots of transgendery books in this search result. If I narrow it to newspapers it seems to be used as a synonym for biological sex.

"There may not be that many female welders or that many male secretaries, but it is not uncommon for men and women to train in fields that society typically considers nontraditional for persons of their gender." Cherokee County Herald, 22 Feb 1995

There's another Google thing called "wordgram" (I think) that might have useful results. I will try to dig around later.

https://www.google.com/search?q=gender&tbs=cdr:1,cd_min:1900,cd_max:1999&tbm=bks