4 1/2 or older.
A common hunter-induced phenomena, which seems to be worse in TN than many other states, is many our older bucks end up with smaller (or lower scoring) antlers than many 2 1/2 & 3 1/2-yr-old bucks.
The phenomena is called antler high-grading, where hunters selectively kill off the the largest antlered younger bucks (3 1/2 & younger), leaving mainly the smallest-antlered bucks to survive to 4 1/2 & older.
The buck depicted above appears to be a classic example of this.
In an unhunted herd, the average living (surviving) 4 1/2 & 5 1/2-yr-old bucks should have larger, higher-scoring antlers than the average living 3 1/2-yr-old buck. But in most TN herds, especially those under QDM antler restrictions, we see really bad antler high-grading, which eliminates most the possibility of what many hunters claim to want most, i.e. a high-scoring mature buck.
Sadly, to me, it's my observation that the genetically-born overall "best" antlered bucks most commonly get killed in TN when they reach the age of 2 1/2. A few survive to 3 1/2, at which point their presence is widely known, then that buck is specifically heavily hunted, by multiple hunters, over thousands of rut-roamed acres, with that specific buck unlikely to live to 4 1/2.
Growing high-scoring mature bucks cannot happen when we kill off our best young stock.