Tough to tell without seeing his body - 4 - 5, 6 maybe. He's definitely older than the one I posted. The eyes are a dead giveaway on a mature buck - since they don't grow with the animal, they look very big on fawns and young bucks, and as the buck matures, the eyes seem to shrink in proportion to the head. On a very mature deer, the eyes will look tiny compared to the rest of the head.
There are many good discussions on field aging deer online. The sway in the back on this last deer, if it is present at all times generally indicates at least a 5 year old (if I remember correctly), though with just this one photo, this is really just a guess.