About 13 percent of the U. S. population or 38.9 million Americans are 65 and older (U. S. Census Bureau, 2011). This number is expected to grow to 88.5 million by the year 2050 at which time people over 65 will make up 20 percent of the population. This group varies considerably and is divided into categories of 65 plus, 85 plus, and centenarians for comparison by the census. Developmentalists, however, divide this population in to categories based on health and social well-being. Optimal aging refers to those who enjoy better health and social well-being than average. Normal aging refers to those who seem to have the same health and social concerns as most of those in the population. However, there is still much being done to understand exactly what normal aging means. Impaired aging refers to those who experience poor health and dependence to a greater extent than would be considered normal.