I'm no biologist, i think they look at the feathers ?, the spurs are probally the best indicator but not foolproof for the average joe, jakes = nubs, 2 year old usually just under an inch and not real sharp, 3 year old or older 1" or longer and sharp, after that i think for us that are not biologists it's just guesswork. but turkeys can wear spurs down, can break em off etc. so if he was a real tough one with sharp spurs then just say he was a 4 year old