54 years old. Lumbar disc bulge. Can disc go back to normal without treatment? How long will it take?

Bulging discs. Bulging, or herniated discs, typically resorb over time. Treatment varies based on the severity of pain and whether you have any neurologic deficit. Treatment can consist of physical therapy and medications or possibly epidural steroid injections or discectomy for very severe pain.
Healing disk. Once a disk is injured, it heals, but will never be 'normal'. 70% of people with an incident of back pain will recover spontaneously. The human body is amazing in its ability to accommodate degenerative changes.