Animals from a shelter have trouble bonding to a new family. If anything, animals from a shelter can bond too strongly to a new family. They may have trouble being left alone at first so adopt when you can spend a few days at home. Set up fake comings and goings that are short. Give your new pet time to believe that you are a new kind of caretaker that always comes back.
Older animals have trouble bonding to new people.
Age does not affect a pet animal's ability to attach to people. Social animals, such as dogs, cats, horses and birds form new relationships throughout their lives with people and with other animals. A very elderly animal may take longer to adjust to physical aspects of a new home, such as stairs or a dog door, than a younger dog but emotional adjustment will not be hampered by a pet's age. A pet will long to be reunited with his old family. Of course animals miss their families and their old routines.