Walter Updegrave, writing in the January/February issue of Money magazine, has an interesting article on the importance of friends when one retires. I'd link to the article, but it appears that the current issue is not yet online.
At any rate, Updegrave cites research by the Pew Research Center which shows that in addition to sound health and strong finances, friendships are a major factor in boosting happiness during retirement.
Further research by the MetLife Mature Market Institute (which has a great downloadable workbook) supports that view.
It does seem to me that I had a wider circle of friends and a more active social life when I was younger. Right now, I have only a handful of friends with whom I go out on a regular basis. I hardly ever entertain at home any more.
Updegrave's point is that we cannot wait until we retire to cultivate friendships. We need to do it now while we're working, and out in the community. Then we need to keep up with the development of new relationships by socializing and volunteering after we retire.
The Pew report points to religion as one way seniors interact in groups. That probably won't work for me since I tend not to be all that religious. But I certainly plan to volunteer during retirement. Right now, being a CASA volunteer for children, and tutoring reading in elementary schools appeals to me the most. But that could certainly change by the time I retire.
I remember my maternal grandfather complaining as he lived into his nineties that all his friends had passed away before him. It never seemed to have occurred to him that making new friends as he got older was important. That's not a mistake I want to make.