Why are most old people mean?

They may be grouchy because they suffer from chronic pain or discomfort, or because they have become negative, cynical, disappointed, or disillusioned as a result of their life experience. They may also be irritable because they feel socially isolated from their infirmities keeping in their homes much of the time, away from friends. ALso, many of their oldest friends may have already died, leaving them further isolated and reminding of their own mortality.