We used to send in teeth from every buck we shot in MN and WI for cementum annuli aging. While cementum annuli aging isn't perfect, it gave us a second opinion to use along with our educated guesses. We had many of the 100-120" deer we assumed were 2-3 year old bucks end up being 4-6 years old. Large bodied (field dressed 180-230) bucks always tended to be 4+ years old even if their antlers weren't great. The opposite was not true though, we had a few smaller bodied bucks that were older than we thought.
More often than not, we assumed that deer were younger than they were. I have no doubt there are a couple 125" 2 year old bucks out there, but I'd say there are far more 3 or 4 year old 125" bucks that people incorrectly assume are 2.5. Unless a buck had a torn ear or something else that clearly identifies him as a fawn or 1.5 year old buck, it would be pretty hard to definitively say what age a deer is.