He'll be at least 31/2 this season I would guess. I always look at the belly/back and the head, I'm not great at this but I'm learning. Just like us, fat shows around belly/face as they get older, plus with deer the back is sagging. Young deer have arched backs, thin face. Older deer will have a stubby face; short and fat. But I only see that up north. The weather here is warm nearly all year long so certain things to look for will be different than farther north. Like one guy said, teeth are the best way.