It is actually fairly easy to mistake a 9 year old deer for a 3 or 4 year old deer. The giveaway indicators though are the head, neck and rump. Also, muscle tone. The head will continue to have the loose skin, and the eyes will still be squinty, as in other mature bucks. The rump, however, will lose mass, not appearing rounded anymore. It won't be smoothly squared off like a young buck. It will be bony looking. The back may also be bony looking. Even the shoulders won't look so well muscled, and the neck certainly won't. I've noticed also that just like old men tend to get gray hair, an old buck tends to look lighter in color than other deer in the area. Not gray so much, but more of a lighter brown. Often, the hair also appears course.