I don't think getting better with age is true. I don't think it's based on age; I think it's based on circumstances, and, no, you're not alone. I would probably fit that category and I've met at least two others on PC who would likely qualify.

In my situation, I had BPD quite bad in my teens and my twenties. It was largely due to relationships. After my son was born, I won't say it went in remission, the traits were still evident, but they were manageable most of the time. I was able to cope. I had occasional bad days, particularly when my dad died and my best friend left, but I was okay for the most part. I didn't realize it at the time, but it was also largely due to the fact that i had no friends and instinctively pushed away anyone who could possibly become one. I was lonely but stable.

Then, last year, I got in to an emotionally charged friendship and it all came back in a matter of a few weeks and it has been difficult to control since. So, yea, you're not alone.