Agree that telling someone about your past too soon does not make you BPD - but is that really someone you would trust to arrive out of nowhere and be an effective "right hand person" in planning & executing something that was important to you? - someone wanting closely involve themselves in my life too soon is now a massive

for me after the way that my ex drew me in by being "helpful"
But what is 'too soon' ?
Again, for me, stating about your past relatively quickly after a few talks is something I don't consider a red flag. There are as many sane people who had screwed up youths without BPD as with BPD
What I consider a red flag is ...
1) wanting to live together talks after a few discussions
2) mimicking behavior is
3) during discussions you'll notice whether or not they are typical 'black/white' thinkers.
Especially the last one, for me, now when I talk with others is something I consider a big red flag. Either all is good, or really bad. And when then after a 2nd or 3rd time tell you they also watched a match of your favorite team then my bell goes ringing. Not when someone got raped and throws it on the table.
I rather have someone tell me that now, than when you hear that 6 months in when you have a relationship and realize that person constantly pushed those thoughts and emotions under the rug and when you want to become intimate a entire '~ storm' comes loose.