وعُرِّيَ أفراسُ الصبا ورواحله
And the horses and riding animals of youth were stripped of their gear.
Youth is represented as a stage with horses and mounts available for a journey. These suggest the impulses, strength, and movements associated with youth; the removal of their equipment conveys that this stage has passed.
This is more vivid than simply saying “youth ended.” A travel-like scene is created through rider, mount, equipment, and mobility. Its components do not require literal animals and saddles. Their function is to build a coherent imagined scene and evoke associated aspects of the target.