A match keeps asking invasive questions. What do I say?
You do not have to answer, and you do not have to be nice about not answering.
The reflex is to answer because the question was asked politely. Politeness is not entitlement, and you can decline a well-mannered question without being rude.
Lines that work
"I don't talk about that with people I've just met." No follow-up needed.
"That's a bit personal for a Tuesday." Light, and it lands.
"I'd rather talk about something else — what did you get up to this weekend?" Declining plus a redirect is the most effective version, because it gives them somewhere to go.
"Why do you ask?" Useful when you genuinely cannot tell. The answer is usually revealing, and someone with an innocent reason gives one immediately.
And, when you are past caring: "No." A complete answer.
Telling curiosity from something else
Curiosity accepts a no. That is the whole test. Someone who is merely nosy hears "I'd rather not" and apologises, then talks about something else.
The other kind pushes. They explain why the question was reasonable, or say they are just trying to understand, or return to it twenty minutes later in different words. Once someone has been told and does it again, you are not dealing with curiosity.
Watch the direction, too. Questions about your body, your surgical history or your previous name are not conversation from a stranger. Questions about your family, your city or what you were like at school are.
You are not the education service
There is a version of this where you patiently explain, and it is exhausting and it is optional. Doing it once with someone you like is a kindness. Doing it with every match is a job you were not hired for.
If you want a way out that costs nothing: "there are much better explanations online than mine."
When to stop
After the second time you have declined and been pushed. Not the fifth. The pattern is set by then and it does not improve, and every additional message is evidence that they heard you and continued.
Block, and report if it went past personal into abusive. You do not need to announce that you are blocking, and there is no closing statement that will land.
Afterwards
If it left you rattled, that is proportionate. Being asked to justify your own body to a stranger is a strange thing to have happen on a Tuesday evening, and treating it as normal is the part that costs you.