After durarara ends.
Izaya's physical condition:
Izaya is capable of activities of daily living. He can walk, but even crossing his legs hurts (he does it anyway), so running or jumping is completely impossible. He explains the events of Volume 13 where he was hit by a scaffold, had his arms broken, and then was stabbed in the abdomen: the inital blow by the scaffold was actually the worst of his injuries and damaged his entire body, but the pain was blocked by his adrenaline and continuing to fight worsened it. But that's not the problem - the disability in his legs is mostly psychosomatic.