This article is from the Your New Dog FAQ, by Cindy Tittle Moore with numerous contributions by others.
Many people feel that an older, grown dog is better for them. Older
dogs don't require as much attention as a growing puppy does. They are
often easier to housetrain, if not already so trained. They are past
their chewing stage, and have settled down from the usual adolescent
boisterous behavior. Such a dog presents no surprises in its final
size and appearance. It may already have the traits they want in a
With an adult dog you have a much better idea of what you're going to
end up with. A puppy can have the genetic heritage to be aggressive, a
fear-biter etc. and you will not know until the dog is older. It's
also very easy to make mistakes raising a puppy. With an older dog,
the mistakes have already been made and it's generally not too hard to
tell which problems will be easily correctable.
So an older dog's previous history is actually an asset, not a
detriment. Quite often when a dog is put into a new situation, they
are looking for leadership and will attach to you almost immediately.
Even breeds known as "one-person" dogs will accept a new master rather
easily. For example, observe the relationship between a blind person
and a German Shepherd guide dog. These dogs have been through at least
3 homes before they're matched with their blind people.
The research on bonding that is most often quoted (Clarence
Pfaffenberger's _New Knowledge of Dog Behavior_) is almost always
misrepresented: i.e. the puppies in those studies were deprived of
_all_ human contact until they were older; the research had nothing to
do with how well dogs that have bonded with some human or humans
transferred those bonds later on.
An additional benifit to adopting an older dog is the truely wonderful
feeling one gets when the dog comes out of its shell and bonds with
you. The bond feels special, particularly when it is an older dog that
no one wanted. The rescue and subsequent bond with that dog is strong,
lasting, and special.
Older dogs are often not adopted from shelters because many people
want puppies. It is wonderful when one can come in and offer a good
life to the older dogs.