Put him on the ground, get his lower jaw and we will see.
Don't think he's as ancient as everyone thinks he is.
Tooth aging is far from perfect. It is interesting to put several approaches together fore deer aging. We put out cameras and try to age them, look at teeth, and have a couple years of history with a few deer and still don't really know how old they are.
I shot a doe once that I was made aware of when she picked up a rock and started chewing on it behind me. Heard this weird sound, turned around, and she was just chomping away and eventually spit out a golf ball sized piece of limestone. Not sure if it has some sort of mineral in it she needed, but it was bizarre. Anyhow, she wasn't an old deer, maybe 3 and her teeth were worn dang near out. I'm guessing the rock chewing did it.
Point being:
What they're eating has a drastic effect on tooth wear. Agree that it's a far from perfect technique. Agree 100 % that it is not a 'perfect' technique, but when combined with other physical features of the buck, would give us a much more accurate idea of the age of the animal.
In the picture provided we have but one view and it is of limited value. Until we can see a broadside picture of the animal...it is not really possible to determine the animals true physique.
Its a Mature animal...no doubt. But the amount of belly drop, back sway, roman nose, etc....simply can not be seen. I don't see any 'loose' looking skin/hide on the animal (in this pic).
The eyes are not 'squinted' (as with many really old deer). We can't see if the buck has a 'dew lap' under its chin/jaw (often present on healthy older deer). The 'gray' some say they see...appears to me to only be lighter (possibly yellow colored) hair, not uncommon.
The enlarged looking knee joints can be a product of the terrain the buck lives in (rocky, rugged terrain takes a toll on joints).
Then we have to consider that a buck (unless under high-fence/managed) is unlikely to live past 6-1/2 yrs of age most places (normal hunting pressure). So the idea that this animal is ancient or 7-9 yrs. old becomes less likely.
Without having more to go on than a single photo, I can't get into the 'post mature' camp with this animal. To me it is not CLEAR that this animal is any older than 5-1/2 to 6-1/2.
Most folks can accurately 'guess' the age of bucks from 1.5 to 4.5 years. After that...even experienced outdoorsmen/biologists have trouble 'accurately' hitting the mark IF they have no other history with the animal. Of course, that applies to me too. That is why I would want to see other pictures of the animal and know more about the habitat.