It's one thing to live a long life, but if you want to live a long and vibrant life, you're going to need a vibrant and sharp mind. The brain, like the rest of the body, needs exercise to avoid becoming sluggish and even disease-ridden. A study of nuns found that the more educated women had fewer instances of Alzheimer's disease. And even autopsy analysis found that while a particular brain may have exhibited signs of the disease, the effects weren't obvious in the women who had challenged their brains and had other interests outside their work [source: Roizen and Oz].
The brain needs to be challenged to keep neurological pathways open. Learn a new language, read or even simply practice awareness of your surroundings: smells, sounds, visual input. The old adage "use it or you'll lose it" has validity when it comes to your mind.