Every region is going to produce different attributes that will show a deers age.
In this area there's a standard progression for most bucks.
.5 years old- Buttons. early born fawns will have larger body size and might have bigger more noticeable buttons. When compared to thier sisters they are bigger and tend to have a longer snout.(ELEMENTARY)
1.5 years old. These bucks can be anywhere from a 3" spike to a little 6 or 8 pt. depending on when he was born and what kind of nutrition he has gotten, and of course his genetics. 1.5 yr olds can be rather large in body size, but are generally skinny throughout their body.( THINK MIDDLE SCHOOL)
2.5 years old. These bucks usually have some body mass put on in their shoulders and base of their neck. Their racks aren't very massive, but have probably started to show their general frame that they will carry for life. Points will vary, but a 15" 8 pt. is probably the most common healthy 2.5 year old where I hunt.(THINK HIGH SCHOOL)
3.5 year old. They've put more mass on their body and will start being seen much less in the daylight hours. Their racks can be impressive and will start to gain more mass. Their "waist" will still be slim, their faces will generally be "pretty" w/ a lack of scaring and grey hair. (THINK COLLEGE)
4.5 year old. Their body will be more barrel shaped, and they will take on a more worn out appearance in their face, ears. Their racks tend to be more massive then the year before and might just have more points. Look for "junk" around the bases too.(THINK late 20's- early30's) They're getting into their prime.
5.5 year old. Very similar to a 4.5 yr old. Antler mass is at it's peak and they're thick throughout their body. They are grayer in the face, and the ridge of their nose will be more distinct then prior years ( Roman Nose). The body may have a "pot belly" appearance and the rack will have more "junk" on it.( think late 30's early 40's)
6.5+ Racks will begin to lose mass, and typical framing that they had in the past. Some points will be deformed or mis shaped and might show more edges then before. They won't lose body size, but they will probably be rough looking with worn out parts. Face coloring might be gray and the nose bridge might be pronounced. They tend to have pot belly's too.( think 50+)
Teeth are used as a general estimate of age, and they can only be looked at with dead deer. Molars will wear with regularity assuming that the deers diet is consistent with what biologists expect it to be.
here's a buck that was estimated at 7.5 he dressed out at 198lbs and was shaped like a big barrel. Notice his mule deer like appearance. His rack is not what it used to be, but no one is really sure what he looked like in the past. He was shot because his foot was swollen and he was having trouble walking. He was missing teeth in the back, and depending on the winter, it could have been his last.
Just like old guys have problems with things, old deer will too.
I guessed 4.5-5.5 on Dove hunts deer b/c the rack fit right into that age estimate. It is massive at the bases, and has a lot going on with points. It might not be wide, but width isn't an age characteristic all of the time.
His uniform belly line says that he is at least 4.5 and he doesn't have a pot belly so he's probably not older then 5.5. Assuming it's an eastern shore of MD deer it should have good nutrition from ag fields, and it doesn't have to climb hills. The dark knob on his chest made me think 5.5 b/c it just looks worn out from many days of bedding down.
I think it's safe to say that he is going to win a few fights this year and should do his share of breeding.
In theory the mature and strong bucks will breed the majority of the does in an area. If there are too many does then the rut will last until they are all bred, and it will take a toll on the health of the bucks and the herd. Late born bucks will always be a few steps behind in the calendar of life, but it doesn't mean they won't become mature "alpha" bucks.
All of this is my opinion based on time in the woods and basic knowledge of deer biology. In the end it's mostly a guess, b/c there are no guarantees on live wild deer.
trail cameras and shed records really help guess the age of a deer, but again, it's all a guess.
-D