When my Mom retired at age 60 she had so many interests, hobbies, volunteer, etc that she was never home & very happy. I am more of a homebody & when I did not work at all I really missed it. I think the big difference is that I am choosing to work but do not have to be up at a certain time, etc. I am totally in charge of my schedule. My hubby did not think he would ever go back to work but about 2 years in he is working p.t. as an engineer. He is a lot happier now. I definitely believe that for many people they enjoy working p.t. if it is something that they love and not a crappy job. When my FIL retired from a job he hated he was offered a p.t. job that was very different from anything he ever did & he loved it. He did not need the $ but did it until age 78 because it was so much fun for him. Once it stopped being fun he quit.