I've eaten them up to 4 years old. You just have to cook in a low and slow, moist method. I did pressure cooker as it's quick. Lots of folks do the crock pot. There are great recipes here in the meat bird or recipe section for cocq a vin, (I'm sure I misspelled that horribly) the traditional French way to cook older roosters.
x2 - Just be aware that if you're not used to eating home grown chickens, especially older ones, they are not like what you buy at the grocery store. They have a lot more texture and flavor. Once you get used to it, it will be hard to go back to the store-bought stuff again. Kind of like eggs.
