I am approaching this issue from the perspective of a spouse rather than as a child of a person with BPD. And we are perhaps older (53) than some of the other spouses who have responded to this question.
In my case, I think that some things are better with age, possibly because the young male testosterone issues have decreased. In the earlier years, my husband tended to react to every perceived threat, insult, challenge, etc., in a physically aggressive way. He's still not really caught up to his actual status physically (meaning that he still has a rather inflated idea of his ability to kick butt) but he is less inclined to let his rages spill over into risky physical conflicts. So that part's easier for me.
He's still awesomely self-centered and clueless about how he impacts on his family. And as I get older and want support through the inevitable trials of life, I find myself feeling sadder about how incapable he is of letting someone other than himself be the focus of attention, and how much I long for a partner who is actually capable of empathy.
But at least I find myself less anxious about him letting his rages turn into public conflicts. I guess that's better(?)... .
For some people, I do think that those with PDs soften with age. My FIL did. At his funeral, the older ones still had painful memories about him, while the younger ones commented that they got to experience the "more mellowed out Joe." However, none of them realize that their dad had a PD. They just thought he was "difficult". My MIL's comments at the burial site were: "Now I can say what I want. And, now I hve more closet space." Yet, no one seemed to grasp what her words really meant, nor did it make them question that their dad had anything seriously wrong with him.
My H has BPD with traits of NPD and paranoia, but he has gotten worse with age for two reasons... . Alcoholism (which his dad did not have), and Testosterone cream (which H insists on using to restore his testosterone levels to a teenaged boy.) The sad result is a raging man in his late fifites who will never mellow. We're separated and I've never been happier and more relieved. I'm filing a restraining order because he barges in whenever he pleases, and recently called 47 times in one night... . Plus when I would no longer answer the phone, he started calling our children's phones multiple times. And, he left a threatening message on one son's phone which has been given to the police.
Those who don't know my H very well (which is most people), will think he's just a regular guy. There are generally only three types of occasions where his BPD will flare up in front of outsiders or relatives... . when he's angry at me and others happen to be around... . when others have said something or done something that really annoys him (like express a different political view)... . when he's non-stop talking, he has no filter, and he'll say inappropriate things.
But, since he doesn't really get close to many people (he hasn't had a best friend or anything like that in over twenty years), and he hadn't kept in close contact with his relatives, most outsiders have no idea of how he can behave. Therefore, he easily convinces some of them that he's a victim, the world is crapping on him, etc). Ugh.
