I'd guess way over 4.5 to the point of geriatric. My theory is that tooth wear at old age prevents them from eating as much hard mast & woody browse as they did when younger, plus the waning appetite that accompanies old age so they don't have a lot of excess weight to carry them into spring green up. Then since their bodies are beyond matured, they grow antlers earlier than most younger bucks and with lots of mass. That in itself is another nutritional expense. I don't get to see many bucks that old. They don't usually live long enough. I see it fairly often in does though, and used to see it quite a bit in cow elk when I lived in NM.
Here's an example of such a buck I had around a couple years ago. Super old buck. You could see his ribs and hips like the one in the OP.
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