Not to go against the grain but he looks like a tip of the pyramid promising 3.5yr old to me, although I wouldn't be surprised if he was 4.5. Really hard to say without history but I'm leaning 3.5.
Here's my thinking. He's way to clean to be old. No scars or tufted hide or wrinkles/folds. His face is sleek & slender with no sag whatsoever in his jowls. His tarsals aren't very bushy and they're barely stained. He's got dumbo ears that indicate he's smaller stature than he looks, and the video of him with that 2yr old reinforces the notion because he's barely bigger than the 2yr old. He's also hitting a mineral site and aggressively guarding it, something a fully mature buck likely wouldn't even be interested in this time of year because his body doesn't need the minerals. A young & growing buck very much needs those minerals. A 2yr old also wouldn't be likely to encroach on a truly mature buck like that, either. Those two bucks are closer in age than first glance would suggest, peers if you will who are bachelored up.
So all things considered I think you're looking at a rare gem of a young buck right there. Just my opinion though.