I stopped working in August of 2011, applied for SSDI in February/early March 2012 and was approved 11 weeks later. I was under 50. I did have a lot of documentation from my therapist and pdoc that I was unable to work and 2 hospitalizations in the recent months before I applied. I think those helped. I think my former employer helped too if they were contacted; they were totally on my side and saw how hard I tried to come back (I lasted 4 days).

Fast approval is possible but knowing that you will be approved ahead of time is impossible. I think they are giving you the worst case scenario but it's hard to know what the best case would be.