You definitely could tell whether he had one if he'd had previous MRIs.

You can't tell the date of a herniation or a bulge, ohter than degeneration being noted, meaning old enough to start arthritic changes. Radiologists would say it's not a "NEW" injury if there's degenerative processes going on. but a cyst, I'm not sure about that.

I know a friend who had a cancerous tumor was told the age of the tumor (7 years) by its size. So not sure on cysts. Ask his doctor.

Back pain is miserable pain. he can't help being grouchy at times. I understand.