4.5+ he's in his prime. He's got either got poor antler genes or he's short on protein and minerals. That body is not the body of a young deer. The lack of muscular definition could be from plenty of food but a lack of protein, or heavy fluffy hair. Either way, he is NOT 2.5, almost certainly not 3.5, and possibly over 4.5. Unless you get lucky, don't count on him being any bigger next year.
That buck is cold and has his haired "fluffed" to help insulate him to keep him warmer. Many people will over-age a buck when they see this. Same happens when a buck is displaying to show his dominance. I always age bucks more carefully on cold morning. Same bucks can look 1-2 or more years older on a cold morning. Many a mistake has been made by people doing cull or management hunts on those same days.
I will agree that he has poor antlers for his age, but I think he is 3.5 max. Seeing a pic of him when he does not have his hair standing up will change the way he looks a dramatically.