As misscath007 says, you have to have worked and earned enough credits over the years to get Social Security disability:

Work History Requirements for Social Security Disability Insurance ? Special Needs Alliance

I think California SDI is non-work related disability; if you were in a car accident, say, and is usually only temporary until you can get back to work: http://www.edd.ca.gov/Disability/About_DI.htm

It can be extremely hard to get a long-term or permanent disability designation, the younger you are, unless it's an obvious physical accident or problem with a job having let you go because of your disability; if you just "quit" your job because it was too stressful for you, you'd have to try to work other jobs and have a history of it not working and a history of the jobs and psychiatrists or other appropriate doctors agreeing that it did not work, etc. The individual does not decide they are disabled and can't work, it has to be obvious (and documented) from their efforts wanting and trying to work and not being able to that they are disabled.