I was dx at 50 and I'm almost 60 now. That's a tricky question, from my research on this dx most in this field believe that it does lessen with age. I've never heard it is "curable" yet, I don't think any mental illness is curable; that's why many are given pills to control their dx.

Personally, I used EMDR to help me with the traumatic events from childhood. BPD is developed due to trauma, and the type treatment used can help one control the symptoms of the BPD. After using the EMDR, I've been able to manage the symptoms (which often arise when I'm stressed). So, I know the markers and go from there. Before the dx I didn't know the markers and often just reacted.

So, in regards to your question, I think one can see less symptoms as they age but this maybe due to maturity and awareness of the markers that arise.
Dealing with BPD takes "work" one must desire to get better and learn how to manage their stressful moments in life. Using DBT has been useful in learning how to change ones behavior and thinking processes. [emoji4]