I diagnosed myself at 23 (after seeing a Zoloft commercial-I had pretty much all the symptoms they mentioned). I knew something was wrong, but didn't really have a term to use for it. When I was 18, I told my mom I needed therapy (for depression, even though I think it truly was my anxiety, possibly coupled with a mild case of depression), and she blew me off.
At 23, I was going to college. Or rather, was enrolled, but not actually attending classes, due to my SA. I finally got up the nerve to talk to a counselor on campus, and, through a lot of tears, told her what was wrong. She agreed with me about the SA and helped me contact my professors.
Fast forward 4 years and I was married to a narcissitic sociopath. I started therapy, and the psychologist agreed with the SA diagnosis and added PTSD (from 2 abusive relationships--especially my marriage).
Then, a couple of years ago, I went to yet another counselor, and she also agreed with the diagnosis. I haven't been to therapy in some time, but I feel like I'm doing okay on my own. I'm sure it would help, but I haven't gotten up the nerve to go back yet.