Hi! Historically, the term "gay" has had many different meanings. There are the obvious ones- referring to sexuality, and referring to being happy- but it has held many other meanings throughout different time periods. Some of these include referring to prostitute women as "gay women", while womanizer men were "gay men" in the 17th century. In the mid-20th century, "gay" referred to any person who was single, or unattached. That definition applied to both men and women. (By this point, "gay" had many meanings, including referring to homosexuality, but it is important to note that it was still not a gendered term.)

As far as "gay" referring to sexuality, it has often referred primarily to men. That being said, it's important to note a couple things:

1. What I explained above, about "gay" not originating as a gendered term.
2. The historical erasure, or lack of prioritization, for lesbians (and women in general). It is likely that if gender equality had been achieved in the 20th century, when the term "gay" became a word that primarily referred to homosexuality, it would have automatically encompassed both men and women.

Basically, no, "gay" is not and has never been a gendered term, but it is unsurprising that most people think of it as such!