Is it unusual for an active person in the mid-30s to have mild thoracic degenerative disk disease?no known trauma.xray also showed old fractured ribs?

No worries: The appearance of the thoracic spine on an MRI may be much different than how you actually feel. There are many published studies that have shown that 20-40% of subjects without symptoms may have positive findings on MRI studies in your age category. Stay active and don't worry.

Thoracic ddd: Unfortunately, we sometimes see even progressive degeneration in the thoracic spine. Fortunately, most people has very little symptoms from this. Surprisingly poor images can go along without any pain, while minimal degeneration sometimes hurts really bad. Thoracic spine pain is difficult to diagnose, although old rib fractures close to the joints, might be painful.