What type of back payments of social security disability in childhood and continued lifetime disability if never had knowledge and have not worked enough to collect all but ssi?

If I understand correctly, you are an adult who has been disabled since childhood and are not eligible for Social Security Disability because you have not worked. My twenty-one year old daughter has been disabled since birth but could not get SSI before she was eighteen. If you are only eligible for SSI you will not receive any back pay. If you are eligible to draw some Social Security (this would be based on one or both of your parents) and some SSI you will receive back pay from the time you applied until payments start. However, it will not be the same amount as one payment per month from the date you applied until payments are receive; SSI will take a large portion of your back pay. The exact math is complicated. You may want to go to your local Social Security office and have someone explain your case, which is what I had to do.