I'm BP II and like a lot of other BP II folks I spend a lot more time depressed than hypomanic. And I often (but not always) am pretty functional during hypomania. So for many years my pdoc's and t's and I thought it was "just" major depression. My first episode was probably around age 8 and they came and went through the years and became very severe mid-20's.
I wasn't diagnosed BP II until this year (age 33). The amazing thing is that somehow I didn't occur to me sooner and my pdoc's never bothered to fully explore it. The pdoc's always just commented on the fact that the only things which seemed to help me were mood stabilizers and AAP's (hmm.....) and the hypomanic reaction I had to Wellbutrin was quickly forgotten. I also think a lot of my hypomanic behavior was mislabeled as anxiety by me and the folks around me. (I do also have anxiety issues, so that clouded the picture.). I think when we came to the BP II dx, it felt like finding that missing puzzle piece that fit perfectly.
In summary, it has been a long journey, but my answer is 33.
Best,
EJ