I wasn't officially diagnosed as anywhere on the spectrum until I was 18 years old. Prior to that, however, there was some speculation. Let me recount the whole story based on what I know, and what a therapist that I saw from childhood until young adulthood told me, as well as what my mother has told me.
When I was born in 1989, autism wasn't well-known for what it really is. During the 1990's, doctors believed that you were either full blown autistic, or you weren't autistic at all. My mother claims that she frequently asked doctors if I was an unusual variant of autistic because I just seemed so autistic. The doctors kept telling her that no, I was not autistic. They didn't know what was wrong with me. I was, however, taught similarly to the "full blown" autistic children during my early school years. I had a lot of therapists, including psychologists, psychiatrists, occupational therapists, and a personal aid who followed me around in school. Interestingly, when I was working on my social skills, I would often be in rooms with "full blown" autistic kids, and one day I turned to a fellow student who was neurotypical, and said to him, "Hey, do you think I'm autistic?" He was so shocked by the question that I had to repeat myself. He thought I was asking him if I was ARTistic, not AUtistic. I suppose people really weren't ready to realize that autism is a spectrum, and that the label can apply to a lot more people...at least, not back then. I'm not sure how I knew I was autistic, but I somehow did.
I was diagnosed with ADHD when I was 3 years old, bipolar when I was 12, and at some point I was also diagnosed with generalized anxiety. It wasn't until I was in my mid-teens that, while attending a therapeutic school, a psychologist came in to assess students and their disabilities and disorders. He pretty quickly told the staff at the school and my parents that he thought I was "Aspergers". At first this was shrugged off, but a few years later, when I was 18, this became more evident. When I was 18 we tried to gradually take me off of my meds to see if I really needed them, and everything became terrible for me. In fact, I had such an almost crazy reaction to being taken off the meds, that my psychiatrist began to realize more and more that there was something more than just bipolar going on. He started to believe that my behaviors while un-medicated were partially due to bipolar, and partially do to Aspergers Syndrome, and I was quickly medicated once again.
In more recent years, my parents and I have started to believe that I may be more typically autistic than classically asperger's, and since the official name of the disorder has changed to "Autism Spectrum Disorder", and Asperger's technically no longer exits as a diagnosis (at least not in the DSM anymore), my diagnosis is technically "High functioning autism". So that's what I say. I'm autistic.