Started treatment at 17 (I think), first dx was psychotic disorder NOS, then psychotic depression, then bipolar NOS, then it was kinda a shyt show back and forth of bipolar I and all the specifiers, schizoaffective-bp, and schizophrenia, adding PTSD, BPD, bulimia/eating disorder-unspecified, and ADHD along the way with an interesting misdiagnosis of DID at one point.
I don't really know when my "first" BP episode was as I was always all over the place and was really, really out of it in my teens especially later (if someone asked me about a teacher I had for 3+ semesters in high school I wouldn't know who they're talking about), but my first full blown hospitalization level mania was when I was 18 (10 yrs ago, where they said "Yeah, BPI")