Age

The length of time a person has existed. Of medical significance in diagnosis and in determining treatment, a person’s age is usually measured chronologically, but it can also be measured in terms of physical, mental, or developmental maturity. The age of a fetus is measured in terms of gestational age, which can be assessed accurately by ultrasound scanning. In children, the most useful measure of physical development is bone age (degree of bone maturity as seen on an X-ray) because all healthy individuals reach the same adult level of skeletal maturity, and each bone passes through the same sequence of growth. Dental age, another measure of physical maturity, can be assessed by the number of teeth that have erupted (see eruption of teeth) or by the amount of dental calcification (as seen on an X-ray) compared with standard values. In adults, physical age is difficult to assess other than by physical appearance. It can be estimated after death by the state of certain organs. Mental age can be assessed by comparing scores on intelligence tests with standards for chronological age. A young child’s age can be expressed in terms of the level of developmental skills, manual dexterity, language, and social skills.