1. A ray processing method, comprising: traversal processing of a ray, comprising at least one instance of selecting a traversal unit having a greatest age from among traversal units configured to process a traversal of the ray, wherein an age of each of the traversal units is determined based on ages of rays that are scheduled to be processed by each of the traversal units, respectively, and wherein an age of a respective ray, among the ages of the rays, is determined based on a number of traversals of the respective ray previously processed by the traversal units, and processing at least one traversal of the ray by using the selected traversal unit, the age of the ray being incremented after each processing of the traversal of the ray; and upon completion of the traversal processing of the ray, outputting a result indicative thereof, and deleting the ray and the age of the ray from the selected traversal unit, to decrease the age of the selected traversal unit.