ORIGINAL: huntingson
Unless you have the teeth scoped or the eye lenses dried and weighed, you have no idea beyond 3.5 years. You can tell by the jaw whether the deer is a fawn, 1.5, 2.5, 3.5, or older. That is it. Beyond that it is a guess without the processes I mentioned earlier.
There are other signs that you can go by that make it more than just a guess. I'd call it a highly educated guess for some. Personally, I look at the whole deer. The shape of the body and face, body weight, antler mass and characteristics, teeth wear and size and wear of the front hooves.It helps if you've seen the deer over a couple of seasons.