Ok, I am an editor. It is my job to pronounce on how words can and should be used, so I have a little authority in this area.

They as a singular pronoun makes perfect grammatical sense. More than that, I guarantee you’ve used it yourself. Easy example:

You sit down at an empty table at a cafe. You go to put your bag on the floor when you spot someone has left their coat. You call the waitress over. “Someone left their coat!” you say. “Thanks for telling me” she says. “I’ll put it in the back in case THEY come back for it before closing. Otherwise, I’ll put something on our social media and see if I can find THEM”.

We’ve always used they/them to refer to someone when we don’t know their gender. We do it so naturally that you probably didn’t even realise, but it’s not incorrect to say. Someone using it because they don’t identify with a particular gender is a very logical step.

I’m not telling you how you should feel about gender neutral pronouns, but it’s perfectly correct language usage and I will fight to the death to defend the good name of grammar.