I have cooked hens, but generally up to a couple of years old max.
Many years ago someone gave me two ancient hens they didnt want to eat. Plucked them, then hung for a few days, then dressed and slow cooked for about 8 hours tried them but tough, then slowcooked again for about 8 hours, tried again, then roast and tried again, then slowcooked again for another day...... and my teeth still bounced back off meat that was like india rubber
Can't remember if the dog could manage it, but it was a lab so probably gave it his best shot.
