As far as I know, the person has never revealed the gender, so you should avoid assuming one way or the other.

I completly agree that pointing out trival grammatical mistakes are useless or even detrimental,
because people learn a lot from mistakes.
This thread should be the place to write freely without fear of being graded by someone.
There are few places in this society where any kind of mistakes are allowed, but that is not a good thing especially regarding to learning language.