Heres the way I do it for my area. (North Central PA)

1.5 - look like does with antlers. Antlers are typically small and usually 6 or less. Basket racks or underdeveloped racks. Body is skinny, legs are long and lenky, stomach is skinny, neck is small, back is flat across the top. Shoulders are skinny. Tarsals are white.

2.5 - Body starts to fill out, neck begins to thicken, shoulders begin to take shape, stomach fills out a bit more, but the back remains flat on top. Antlers begin to show potential, but remain typically small. Tarsal glands may show a slight coloration. Legs seem to fit the deer more appropriately but still look a bit lenky.

3.5 - Body has filled out and the legs look proportional to the body. The belly begins to sag, the top of the back shows a slight sag, the neck has filled out, and antler potential is showing. The forehead shows a wider head than younger bucks. Shoulders have filled out and muscular definition shows. Tarsal glands are brown and look fairly dark.

4.5 + The body is large and thick, as is the neck. The back shows more sag and the tarsals are very dark. The belly looks large and bulges on the sides (depending on time of year) Shoulders have fully developed and seem thick. Legs look short compared to body and deer has reached its full body size (typically)

Those are a few off the top of my head that give me an idea of how old the deer are.. Hard to do it off the hoof, the best way is to see some deer, guess there live age then have a guy from on here give the actual age after a kill.. Doing is always the best way to learn..

(I've probably forgot a few ways, this is just off the top of my head so feel free to add to the list)