pretty good explanation for AFTER the kill.
"Young deer are easy to tell. They have smaller heads as fawns and slender heads as they get older. A young buck will have a face that resembles a does. His body will also look like that of a doe, being long, lanky and slender. His neck is skinny and his front legs will appear close together at his chest.
Middle-aged deer become much more filled out in the body. They lose the skinny face, and their bodies look more like that of a racehorse. Their bodies are now developing and they are putting on weight through their shoulders, neck and rump. The best way that I determine the difference between a three and a four year old is by looking at the deer from the side and paying close attention to where the stomach meets the body by the rear legs. If the stomach still goes up it is three. If it is straight to the legs, it is four.
Mature deer will stick out as mentioned above. Unfortunately, most deer never reach maturity for many reasons. But seeing one will really make a lasting impression. They are much heavier in their bodies than middle-aged deer. Their chests become deep and their legs appear to be short and farther apart at the chest. Their faces become full and their necks are now flabby. Their stomachs are now big and their backs are sagged. They have lost that look of a racehorse. Look even closer and you"ôll even see wrinkles at the base of their ears. They look old and it is obvious."
this is an exerpt from: http://www.keithwarren.net/stories/111603.htm