Supposedly BD can manifest anytime from childhood on into the adult years...20's...even 40's. Personally, I believe I had bipolar symptoms as young as age 4. I experienced a very odd, extremely intense type of rage at that time. I definitely had symptoms of both depression and mania when I was a teen.
That said, it seems that many people don't show bipolar symptoms until adulthood.

As for med-induced BD there seems to be quite a controversy over it.

Add in hormonal/endocrine changes and moods can go wild. Menopause for me was sheer hell as far as extremely severe anxiety (which my pdoc referred to as 'dysphoric mania').
Truthfully, what do I think? I think that psychiatry is a new and inexact science. Yes, there are certainly some givens, but there sure is a lot of inconsistency with regard to diagnosing. I believe that one day, eventually, many years from now, gene therapy will be the treatment for mental illness and meds won't even be used at all - at least, not the meds we know of today.
I very well understand how and why you are questioning your diagnosis. Are you thinking that perhaps you have unipolar depression?