Behaviour Change after Retirement.

My Father is 70 years old retired government servant. After his retirement we are noticing changes in his behaviour, whenever any relatives or family members try to talk with him , he is not interested in listening anything and keep looking in his mobile all the time. When we suggest anything then he would not follow it but if outsider gives him any advice then he would listen to them and act accordingly. He doesn't like to stay at home and always find reasons to go outside and most of the time spend time out of the house. Whenever we go any reason for dinner, he finishes his dinner fast and start taking with waiters and hotel staff but don't talk with us much. He always thinks that anything suggested by outsiders even stranger is right and never listen to family members or any relatives . Note : We are financially stable and having very stress free life and no one from family ever scolded him for anything. We don't understand the reason behind behaviour please give suggestions.