To help understand data about children – such as child health and mortality – statistical organizations classify the ages of babies and children in a more standardized way. The environments that people live in as children – or even as developing fetuses – combined with their personal characteristics, have long-term effects on how they age. Older children definition Older children means patients who are 18 to 21 years of age, inclusive. With babies and young children, we count their age in weeks up until 6 months, then months up until 2 years. Our research shows that this is how people talk about their child's age. Current definitions of old age include official definitions, sub-group definitions, and four dimensions as follows. Most developed Western countries set the retirement age around the age of 65; this is also generally considered to mark the transition from middle to old age. The United Nations World Health Organization, headquartered in Geneva, Switzerland, has established new standards for age classification after measuring the global human fitness and average life expectancy. Curious about the World Health Organization's official age categories? Discover the global health definitions for youth, elderly, and beyond in this comprehensive guide. When possible, use a specific age or age range. Age range designations vary among organizations (American Medical Association, American Academy of Pediatrics, etc.), so ask for specifics and definitions if a general term like adolescents is used. The United Nations Convention on the Rights of the Child defines child as, A human being below the age of 18 years unless under the law applicable to the child, majority is attained earlier. We sometimes refer to children between the ages of around 8 and 12 as tweenagers or tweens, but after they turn 13, they are real teenagers. We use the adjective teenage to describe them and things connected to them: The band is popular with tweens. They have three teenage children.