Fighters that got old over night?

Getting stopped tends to speed up aging in the ring and having tough wars. Hearns got older fast once he was stopped by Barkley, and the Hagler knockout slowed him down also. But he was one guy who was such a motivated guy he actually improved where some guys just get worse. I think knockout losses age a guy the most as well as ring wars. Also, taking long breaks between fights. If a guy can stay near the same weight he has fought and not take too much time off without losing by knockout, he can stay going for a long time. Hagler was affected more by the Hagler/Hearns war than Hearns was, which was surprising. The punches he took hurt him more than the knockout Hearns got since Hearns was more tired than knocked cold.