As a wildlife biologist long involved in quality habitat and wildlife management there is one "hunter" question that pleases me more than any others, "How old is he?" As opposed to "How big is he?" This especially if the buck is standing about a hundred yards away and the hunter is making up his mind as to whether or not he or she should pull the trigger.
There are basically two ways to age whitetail bucks. One is looking at them while they are alive and the other is looking at their lower jaw to determine their age by tooth eruption and wear, after they have been harvested.
Let’s take a look at "field aging" live bucks. The best tips I can give at aging whitetails bucks come from experience, I have been involved in field aging whitetails for over 30 years as a professional wildlife biologist/manager as well as a guide, plus quite a few more years as a hunter. Deer age much the same way people age and it's best to think of them in terms of immature, almost mature, mature and old.
1. After a quick glance at the antlers and making certain both main beams are present, I totally disregard them and look much more carefully at the deer's head, neck and body to determine where he falls within the immature, almost mature, mature and old categories. Besides antlers are generally not a good indication of age, beyond the very young.
2. Essentially immature refers to yearling bucks, those which are 1 1/2 years old; almost mature refers to the 2 1/2 and 3 1/2 year olds; mature refers to the 4 1/2 to about 6 1/2 year olds; and old to those 7 1/2 years old and older. Yearlings, or immature bucks have slender necks and bodies. They remind me of looks and behavior of 12 to 15 year old boys. And their hocks (tarsal glands) are usually cream-colored during the rut.
3. Almost mature bucks, those that are 2 1/2 years old, have a little better muscle tone, their body is starting to fill out. They are a bit deeper through the chest. Their skin is tight about their heads and neck. During the fall their necks may be fuller than immature bucks, but they aren't truly swelled during the rut. Three year olds tend to have more swollen necks, but usually not swollen past the point of their jaws when they are looking at you.
4. Three year olds are to me the toughest to judge. But remember deer are individuals. Some tend to "grow up" quicker than others. These bucks tend to move with a certain grace and fluid motion they move like a college athlete. They tend to have a straight line back and belly. Their tarsal glands, hocks, during the rut show a little brown and some may show quite a bit of color. I am convinced in watching whitetails throughout North America, that 3 1/2 year old bucks do more breeding than any other age class during the rut, this as a whole. Thus, they are quite active during the rut!
5. Mature bucks, those which are 4 to about 6 1/2 years of age, generally have muscular bodies, they are deep through the chest, have well developed and swollen necks, they tend to look like they're "front heavy" meaning they look all neck and shoulders. The skin about their face is starting to sag a bit so they have jowls hanging underneath their jaw. With many mature bucks it looks as if their legs are short compared to their body. During the rut, not only will their necks be greatly swelled, their hocks (tarsal glands) should be stained dark, not only at their hocks, but all the way down the back side of their hind legs to almost their hooves. They move like professional athletes, who have been in the pros about five years.
6. Old bucks? Unfortunately far too few hunters get to see both mature and especially old bucks. These deer to me are by far the most interesting bucks to hunt, the 7 1/2 year olds and older. They have survived several hunting seasons they know the ways of hunters. Some biologists will tell you their antlers are past prime by this time. I don't necessarily agree. Older bucks tend to add "character" to their antlers, perhaps "gnarlyness," perhaps extra points. But if on a good nutritional diet it's not uncommon for old bucks to develop their best antlers ever. I've seen numerous known age 9 to 11 year old bucks grow huge antlers, by far their best racks ever, if they have plenty and high quality forage available. As to field aging old bucks, they move like old men. They walk like they have arthritis, their backs are swayed a bit, and they have a pot-belly. Their skin looks like they're wearing clothes a size to big, especially around their head and face. Usually these older bucks have well defined jowls. To me old bucks remind me of old grandfathers, yet still the kind who truly enjoy interacting with their young grandchildren.
Why age and keep records of whitetails? Only through maintaining age, weight and antler development measurements can you evaluate the worth of any management program, by comparing same aged deer from then to now. In order to truly evaluate the worth of the program you must compare data from same aged deer.
Bonus Video: Age This Whitetail