I had a lot of problems in my teens and early twenties and then decided not to have any more friends. I pushed people away vehemently, and was able to cope, fairly well most of the time, for over twenty years. Two years ago, I made a friend, the first in forever, and everything came crashing down. I was put back to square one. So I guess your answer is yes. For a very long extended period of time I was fine. I personally believe that age has little to do with BPD as circumstances. If our circumstances allow us to function well, we do. When other things come in to play, we revert. Also, according to the DSM, it is very common for people with BPD to go for extended periods of time with little difficulty and then have a relapse or revert.