You may receive benefits when you are adjudicated disabled;  it's not only an old-age program.  Benefit payments for disability are based on your average earnings.  In most disability cases,  you must have worked 20 quarters (that is,  5 years) directly preceding the onset of disability.

You are disabled if you have a physical or mental condition(s) that prevents you from engaging in any substantial gainful employment and the condition is expected to last for 12 months or to result in death.  Medical evidence is necessary to prove your inability to work.

SSI stands for Supplemental Security Income.   It's a program run by Social Security.  It pays monthly benefits to the elderly,  the blind,  and people with disabilities who meet certain income requirements.

Yes,  however,  your Social Security disability benefit will be reduced so that the combined amount of the Social Security benefit you and your family receive plus your workers' compensation payment does not exceed 80 percent of your average current earnings.

Yes,  by going to going to your local Social Security office and requesting Form SSA-7004-SM-OPI,  Request for Earnings and Benefits Estimate Statement.

Yes, the combination of advanced age,  severe mental or physical impairment,  and limited work experience can seriously affect a Claimant's ability to perform a significant number of jobs in the national economy.

Social Security will consider the combined effect of all your disabilities and impairments without regard to whether they are work-related or not.  If there is a combination of severe medical impairments will be considered to determine if you are disabled.