Few prejudices in Western society are more powerful than those concerning aging. Until recently, we have assumed that the story of aging is one of loss and decline. But there's an entirely different truth. Yes, you can teach an old dog--or even a sort-of-old dog--new tricks. Is there a secret to staying young? It turns out that there are many, and they all begin with nurturing our existing relationships to foster brain health, keeping us happier and...