You seem to be very knowledgeable. Are you now studying to be a therapist? Don't take this the wrong way - so if you don't ID what is with yiur name and y r u here? If you don't ID I would think you would go back to a normal existence and leave this all behind.

I think what I heard from your posts is everyone is different. Everyone has different parts of this. An example I do not do drugs, I don't self harm and except during really bad times I don't drink too a drunken state. I have recently but with my history it is a phase not an addiction. I have had it checked out by many people. I have not attempted suicide. I don't have random acts of sex with many lovers.
I had 13 straight years of bullying. I had a narcissist mother and an absent uncaring and unloving father. That is years of bad stuff. That takes time and $$$$$$$$$ to get over. I was a single widow with two disabled children that I still support. I could go on. I get you are young and have not lived a very long life so that limits your wisdom. When I was young there were onily two dx - bipolar and schizophrenia so when I was young there was no DSM anything and no treatment so yes NOW people are diagnosed and treated when they are young not then.
I hope I am not being too blunt and harsh with what I am saying. If you see that in the post I apologize.
You are right there is no interest in finding out if older BPDs get better we were the BAD patients for years. Do yourself a favor call your local psych ward as an experiment and act like you are trying to admit a suicidal 50 year old BPD and you will really get told how therapists SEE us. It is not pretty.