That job you mentioned had to be one that you paid into Social Security here in the US. SSDI is like an insurance plan, if you don't continue contributing, than you lose eligibility--as Janke said usually it's 5 years (at the latest) after you stop working.

SSI is essentially a welfare program. If you live in another country than you do not qualify, no exceptions. If you move back to the US and decide to continue living here, than you'd qualify for SSI.

At age 29, if you've been living outside of the US for 15 years, I would assume you have never paid into Social Security? If there is enough medical evidence that you were dealing with such severe psychiatric issues before age 22 that kept you from working, and you had a parent that was eligible for SS benefits, there might be a possibility of qualifying as an "adult child", but if you held a steady job 2 years ago that alone would likely disqualify you.