The pic you have posted is of a mid June, note the sage and the size of the bucks horns, look for the black patch and black nose,

<img src="http://img.photobucket.com/albums/v650/ldjanos/Antelope05014.jpg" alt="Image hosted by Photobucket.com">

This is a pic of a run of the mill 4 year old, You would be guessing on theleft and far right buck on thier age at that time of year, The buck in the middle is a yearling you can tell by body size and the horn growth.

The goat on the far left is an old doe note the shape of the skull and the lack of cheeck patch.