From managing our ranch and a few others, I have had the opportunity to age a lot of deer on the hoof ….but also been able to see many of those deer that were aged on the hoof killed and then aged by jaw molars and been able to compare the two findings.
Some will argue that aging by jaw teeth is not accurate as well…but it is assuming a plus/minus 2 years margin of error at a max….and is still considered the best standard in the field by every biologist out there. It is still proven to be the more accurate method than not.
The thing to do on this 5.5 year old deer that looks like he is 3.5 on the hoof, is to shoot him and post his molar pictures. I for one would really be interested in seeing those.
I have certainly found that I have, over the years, really missed on aging some deer on the hoof…..and agree with your thoughts. However, using basic guidelines, that have been proven to be much more right than wrong…again on the average as you say..not all follow the rules.

Especially if you get to then look at the harvested deer molars and can compare on the hoof aging vs. teeth aging on the same deer….it sure teaches you a lot.
This particular deer should have been harvested out of the herd when it was determined he was 3.5 and was not improving. …what you waiting on?

I'm being sarcastic of course.
TAMU Wildlife & Fisheries Sciences