My friends JRT looked youthful until, when he 13, my friend ended up with a little pup she found abandoned. It aged him overnight, bless him. I don't know if it was because he couldn't keep up with the little one and got tired trying, or if he just felt he could finally have a break because the next shift was covered 😂 He went from grey but bouncy to little old man with a Zimmer frame and an ear trumpet in an instant 😂