why tell a vet your pet's age? I think it would be unfair to judge a dog's treatment options by his/her age?

You need to tell them their age for several reasons...

A) Nutrition- dogs have different nutritional needs at different life stages
B) Medications- as the dog ages the metabolisim slows down making it harder for them to process one medication over another
C) Organ functionality- Some medications are known to affect organs such as the liver or kidneys. Younger dogs can tolerate this better than older dogs, and drug protocols are changed when dogs are older, to make it safer for the pet

Same thing goes for dogs that are too young.. their immune system or metabolisim may not be developed enough to handle what is being given..it may even harm them

PS The vet can tell the dog's age ( +/- a few years) by a variety of ways such as teeth.. not just if they are adults, but the amount of wear and tear, amount of plaque, lines on the canines etc.. the eyes will have different changes, etc so your doing absolutly nothing by keeping his age a "secret"

why would you want to anyway.. wouldnt you want your vet to know as much history as possible so the most effective and safe route of action can be taken.. It makes no sense not to..

knowing the age is important in knowing if a pet is at good health. The vet can make better treatments and diagnosis knowing your pets age.

You wouldnt withhold such information from your own Dr.. why would a vet be any different?

treatment options are not made "unfairly".. treatment options are given based on what's best for the circumstance.

Its ok if you dont want to tell your pets age.. the vet can get a good idea of the age anyways when he examines the teeth.

Unfair??? So you like to have the Vet guess??? They can get some idea by looking at the teeth but why waste the Vet's time? Treatment is based partially on the age of the dog. Some health issues are more common at certain stages of a dog's life. When diagnosing the Vet takes this into consideration.

Many problems only arise in an animal past a certain age. Also, some medications can have worse side effects for young animals or older ones. Their treatment isn't entirely based on their age, they just use their age to work out the best treatment and determine any complications that may occur.

Sometimes it's not about the vet judging your animal by their age. Age is a very important factor in treatment sometimes. If your pet is older it may be prone to more problems or some medications, like that used to treat heart worms, will effect a dog differently and many older dogs can't handle the treatment for heart worms. It's not so much about being judged, it is more about being aware of the problems that could occur because of their age.

A dog's age is very relevant to it's treatment options. Very young and very old dogs have problems with anesthesia, in older pets there might be issues with the heart, or other organs. In very old dogs, is it fair to put them through a major surgery and subsequent long recovery? In a young dog, for instance, a cruciate ligament surgery can improve the quality of their life for a very long time, in a very old dog, they might not come out of anesthesia, take much longer to heal and have much more pain than if the problem was managed with pain medications.
It's not age discrimination, it's common sense.
I will give you a human example, I recently was in a car accident which fractured two of my upper lumbar vertebra, because of my age, 52, my neurosurgeon gave me 3 months of total disability instead of the usual 6 weeks, because older people, and dogs, take longer to heal than young ones. It is important that your vet have as much information as possible about your dog in order to weigh all the options and make the best decision for the dog.

Treatment options are not simply based on age. There is no discrimination on age. The vaccinations, medications, and procedures that a dog can physically undergo depend on age. Some dogs are too young for vaccinations, some are too old for certain procedures because their bodies wouldn't be able to take the strain of being put under anesthesia. Knowing a dog's age also helps the vet know what kind of ailments to look for. Older dogs have a higher chance of having cancer and tumors, and other age related problems, etc. Age or an estimate on age is imperative in treating an animal properly. Even if you don't tell a vet the animal's age, they can make an educated guess by checking the dog's teeth, and other physical attributes. Having the human confirm that age just makes things easier. It also helps the vet suggest a change in diet if necessary. Older dogs do not eat the same foods that puppies do, etc.
Just like it is important for a human doctor to know our age, it is important for a vet to know our dog's age.

Because certain things can only be given to dogs of certain ages. If a vet doesn't know your pet's age, they won't be able to properly diagnose and treat your dog. Plus, they don't want to be sued for malpractice if they kill your dog because they gave your dog something that's not actually age appropriate for your dog's age, since they didn't know the dog's age.

It's absolutely necessary though.

Eg medication dosage depends a lot on age too. Certain diseases have an average popping up age so the vet needs to know, not the exact age but around what age your dog is.

Well let me put it this way. A one year old dog, vs. a 10 year old dog. A one year old dog may not have shots, and may need them while the older dog has already had them, or may need to get updated shots. The age of the dog, would also point out whether or not some things could be the factor of PAIN, such as arthritis, in the older dog while the younger dog could be diagnosed with something else wrong (my dog's knee cap slides out sometimes for example, while my friend's dog has severe arthritis). Not only that, but the age, like humans, also changes what is happening INSIDE the body. For example, as they grow older they lack calcium and other beneficial stuff that they could have had huge amounts of as puppies. This, will allow the correct dosage of whatever to be given, to allow the dog relief without fear of DEATH. Another example of this reason, would be because giving a puppy the same dose of antibiotics, vs. a full grown 3 year old dog would be severely BAD on the vet's part. Because of the size of the dog, and it's body has not fully grown, or created a full immune system.