Here you go.. Hope he doesn't mind me plagiarizing him.
I have had the privilege of collecting hundreds of samples of teeth from harvested bucks, estimated their ages and then had the teeth lab aged. Even within a local population, the variation is tremendous, and ages are very difficult to estimate based on the appearance of the deer. I have seen small-bodied bucks with forked horns less than 8" long, that any game bio would call yearlings, but which when field checked had 50% tooth wear and came back as 4-6 year olds. I've seen big, stout hog-bodied, sway-backed thick-antlered bucks, that I'd have classed as dominant 6.5-9.5 year olds; but with sharp pointy teeth come back as 3 year olds, including a 29" outside spread 5x5 whitetail and 30"+ mule deer.
When I can look at their teeth in hand, 90% of the time I am able to guess age within +/-1 year. Without looking at the teeth, just field-dressed carcass and antlers, I'd say I'm 90%+ on 1.5 and 2.5; for buck deer 3.5 - 4.5, maybe 70%; over 4.5, I'm lucky to be 50%.
The oldest hunter-harvested buck I've seen from WA was a 13.5 y.o. buck killed in the Swakane late archery. He was a slick 4 point with average mass, about 20-22" outside spread, no trash, a slender face and a straight back. Without a look at his teeth, I'd have confidently called him a 3.5 year old. Based on his worn out teeth, I estimated him at 12+, which the tooth aging validated.
I've known enough bucks that were notable and showed up on the same winter ranges for 7-9 years, to believe that trophy bucks are big early in life. I've only killed 2 bucks that gave me a twinge that I might have killed a great buck before it reached its potential: a 2.5 year old, 22" 4x4 with eyeguards that scored 145, and a 4.5 year old, 31" 4x5 with eyeguards.
Guessing ages on game animals is fun, but without the teeth I maintain it is a game. The bear I killed in September was a humbling classic: a game warden, a game biologist and an extremely experienced successful hunter all estimated him as a 2 year old boar; when he hit the dirt, "he" immediately became a 20+ year old sow (exact tooth age pending).
