That's what cats would eat in the wild, clearly. And he's a domesticated cat, so eating raw meat is not going to make him feral again. Let him eat what he wants. He's 16! Make sure the raw meat is fresh and from a safe source. Store it as if you were going to eat it yourself, and don't leave any lying around in his bowl. Let him eat his fill, then take the leftovers away and throw them out. Although the meat for our consumption is very regulated so that it is safe, do make sure he's wormed really regularly, just in case.