There is no sensible reason to suppose that "gender" should refer only to grammatical distinctions. Perhaps it once did, but if you followed that line of thinking to its conclusion you'd have to speak Anglo-Saxon.

As Matt Ridley puts it:

"I make no apology for using the word gender when I mean sex (male or female); I know it is a word that originally referred only to grammatical categories, but meanings change and it is usefully unambiguous to have a word other than sex for males and females."
"Sex" is one of the most ambiguous and emotionally-charged words in the English language. Occasionally it is used to refer to the distinction between males and females, but most often it means something else. "Gender" - a term which in its grammatical context is in any case almost analogous to "sex" - is the perfect alternative for this particular meaning.

To deny the usage of a word on the grounds that it wasn't used that way in 1913 is both counter-productive and doomed to failure. The phrase "hypertext markup language" was meaningless when Webster_1913 came out - shall we stop using that too?