Thrown off 2nd story roof age 2 ended with severe sprain both legs. pain in legs lasted till now age 27. why do my knees/hips hurt even when bending?

Posttraumatic joints: You likely suffered injuries that may have triggered what is called posttraumatic arthritis, which is the premature development of degenerative changes in a damaged joint. All weightbearing joints will degenerate over time, but a significant injury can accelerate this process. Stiffness and pain are hallmark symptoms. X-rays could confirm the findings.

Thorough work up : I agree that x-rays are a good place to start. A good evaluation to determine if the discomfort is coming from the bones, muscles, or nerves is helpful and can help direct treatment. One cleared, a tailored exercise program developed by a physical therapist will help you find ways to achieve your goals with minimal discomfort.