Social Security and your doctors (most Soc. Sec.) are probably going to have to decide that. Like so many times, your situation isn't clear-cut. If you saw any counselors or doctors before your diagnosis at 19 that discussed your mental health, it would be good to make a note of their names, addresses, and phone numbers and give those to Soc. Sec. during your phone interview.

When do YOU truly feel like your conditions became so bad that you couldn't keep a job? If it was age 16, I'd say that. Soc. Sec. is probably going to say age 19, but I'd give them my true opinion.

This is all very complicated, isn't it? I have been through two cases (two judge hearings) and have come to the conclusion that you can get disability without understanding all the ins and outs of it, so try not to let it stress you too much.