If he's old he'll need to be stewed bc he'll be tough, but meaty. Go to backyardchickens.com (link below) and look up the Butchering and Evisceration Stickie. That's how I learned to butcher my birds. I use a tree and tie them up by their legs with baling twine, which I SWIM in after opening up 400 bales of hay/winter. I super sharpen my knife--a couple of years ago I bought a field dress kit for hunters--and I use safety gloves bc I've sliced myself before. I cut the "jugular" below the cheek and bleed mine out. They are gone is less than one minute and are unconscious in about 15 seconds. After it's a corpse I saw off the head. I usually butcher in multiples of two bc my dogs like the heads and the feet.
He's a vicious bird and needs a death sentence.