This seems to be something I really struggle with. It's not real hard to pick out the old one if there is a group of all ages. But when there's only a few I can almost never age them. How do you do it. Are you looking at the back, where the neck meets the body and size of ears in relation to the head or what?

No sure fire way. I try and classify them as immature (1-2), middle-aged (3-4) and mature. Body size is your best indicator, as well as facial features. In the end, if you just need to kill x number of does, then a doe is a doe.

I look at size and shape of the head and body lines, briket etc.

Like fouz said, if for herd numbers it doesn't really matter if you need to kill x number of does then get after it a doe is a doe.

From our records over the past 7 years 4 YO is about the peak body weight for does, so they should appear to be your biggest ones, past 4 yo our live/dressed weights drop off.