Many people buy fully grown up dogs and then try to integrate them into their homes. Since it is a new environment, they are usually nervous and cautious. They look evasive and apprehensive and can even be a threat to children. Caging them would not be a viable option since it would take them much longer to integrate into the family. The other issue is that there might be resistance from the other resident dogs. So, how do you integrate mature newbies?
It only requires patience and effective guidance. Firstly, you start with gradual introduction to the new environment, provide comfortable space and not a cage, veterinary check up is very important and lastly reward calm behaviour.
It's not easy to have a matured dog but the only way to make it easier is to try from petting, allowing them to be free with everybody in the house because they must surely find a favourite there. Introducing them to things they need to know is the most important thing.
I wouldn't rush it. I would let the dog explore, stick to a routine, and introduce people and other pets little by little until it feels comfortable.