The best way to do it is ask the deer when his birthday is. seriously though, youngerbucks will have sleek bodies and shorter faces. the older bucks fill out. The chest will be bigger, and the body will be stockier, nose will elongate. Also, like people, deer kinda go grey. Look at the nose and face of the deer. if you see one with some grey (not all the time though) u are generally looking at an older deer.