A chicken can be aged without brine, but then the chicken has to remain at a temperature above freezing to age and is subject to bacteria. As has been stated before third world countries do not refrigerate their meat it is hung open air. And you will find the cuisine very tender, you also may pray to the porcelain god if you are not accustomed to it. Meat of any kind will be tough if it never goes through the rigor process. Usually with wild game their is a longer time line before the meat is processed and the carcass goes through rigor. Brine not only insures the tenderness it preserves, and the simple fact that it is submerged and not exposed to bacteria in the air also protects from illness.
When frog legs are cooked fresh they will twitch in the pan. Lack of rigor in reptiles or fish is a good thing because then the meat is firm. The opposite is desired with beef, pork, and poultry. This is why in times before the prepackaged supermarket meat the quarters or halves were hung on serpentine hooks and cut in order of age. Usually 15 to 30 days. When we used to pick up poultry from a meat shop when I was a child the chicken was pulled from a wooden barrel filled with brine. The beef was a cut pulled from side hanging.