As already mentioned, the only way to really tell for sure is a tooth sample. Facial features would make me agree with the 3-4 year old coments, but even that can be hard to judge by. Different areas certainly produce different looking bucks-depends on genetics, feed etc. Used to hunt a spot in Utah that produced very, very large horned deer in just 3-4 years (habitat was picture perfect and the gene pool there was excellent) now hunting further south in the state and deer there are very, very slow to develop horn growth and the gene pool isn't quite as good. Even body size can be deceiving for the same reasons. When they start to get that gray around the muzzle area and seem to develop bigger facial features in general is what I look for in an old deer. Just like people, size (no pun intended) is no real indicator of age.
