Many hunters are curious to know the age of their deer. Anyone can age a deer... to a point.
Look at the third molar (from the front) on the bottom jaw. If that tooth has three "parts," then the deer is 1.5 years old. Note that the tooth might actually look like three separate teeth but has only one root. If that same tooth is made up of only two parts, the deer is at least 2.5 years old.
Beyond that, you can make an educated guess based on wear, but it's difficult to be certain. Factors such as the type of food the deer eats and his genetics play a role in tooth wear, so one 3.5-year-old deer's teeth might wear more than another of the same age.
While it is possible for biologists to make a cross-section cut of the tooth and look at it under a microscope to get exact age, the expense and time involved limit the use of that method.