For frying, the tough older greys can be tenderized using butter- or whole milk. Cut up to fryer size, place in a bowl or pan, and submerge in milk (1% or 2% works too, just takes an extra day). Cover with lid or plastic wrap, and place in fridge for 2-4 days. I like to pour off the old milk and rinse them off after 2 days, then cover with fresh milk. Rinse again when ready to fry. The milk doesn't add any other flavor to the meat, like some marinades do, but leaves them tender like the young ones.