Many people make plans for various aspects of their retirement, but how many plan for their mental health as they grow older? The Journal of the American Society of Neurology reported a study last year showing how to plan to reduce the chances (and severity) of dementia. The report showed that older people who engage in regular exercise experience far less cognitive decline than those who get little or no exercise. The difference in cognitive decline is equivalent to the decline you would expect from ten years of aging.