I started going to therapy when I was 15, for anxiety/self harm/depression. My therapist apparently diagnosed me with bipolar around that time, but never told me for reasons unknown to me, just put it in my charts. Looking back, I thought that mania was stability, and my "baseline" so to speak, I just couldn't understand why I would so suddenly get depressed. It probably started when I was around 11. I was formally diagnosed at 18, and I'm 19 now. It's still weird to me, and I tend to doubt my diagnosis still, even though it makes sense and so far medication has worked wonders for me(lithium, now lamictal)