From the size of that deer's body and the sway back and belly sag I'd guess him at 4.5.

He looks like a great buck, and definitely has good mass and a great spread, but he may be one that just doesn't get very tall. He'll likely get a little bigger, but he should be hardening up in 10 days to 2 weeks so I doubt he'll put on a ton of inches.

Not that it matters because at that size and being a 4.5 year old he'd be getting shot by me no doubt.