Extremely difficult to give an accurate age on that jaw because of the malformation in the teeth. The broken front cusp of the 2nd molar (5th tooth in the mouth) certainly changed the chewing pattern of the deer, as that would have been a painful injury.
But looking at the state of all of the teeth in the mouth, I would have to guess the animal is mature. At least 4 1/2 with a good chance of being older than that.