Some say you are as old as you feel. Still, there's a biologic age that defines "old." With the continued aging of America, the term "elderly" is being replaced with the word "aging."
People who study aging adults are trying to define new age categories. This will help researchers identify risk for illnesses and injuries (like hip fractures) at each age level. Prevention programs can begin before adults reach the age with the greatest risk.
At the present time, the National Institute on Aging (http://www.nih.gov/nia/) has identified the following age categories. These may change slightly with more research:
Pre-elderly: 55-64 years
Young-old: 65-74 years
Middle-old: 75-84 years
Old: 75-84 years (Note: Whether someone is "old" or "middle-old" depends on health status.)
Frail-old: 75 years and up
Oldest-old: 85 years and up
Elite-old: 95 years and up
Centenarians: 100 years and up