Teenager is a numeric term used to describe a person from the ages of 13 to 19 years.[1] Although it is used to distinguish people by the decade of their life, it excludes ages 10–12 even though they are part of the same decade, since the numbers 10-12 do not include the suffix -teen. Instead, people aged 10 to 12 years old are placed in the category of preteen, which was coined to recognize ages 10 to 12 as part of the same decade as 13-19 but linguistically separate due to the absence of -teen. The shortened form of teenager is teen, which is the only recognized form of the suffix used as a noun or adjective.
Although teenager is primarily a numeric age term, it is commonly used to describe a person in the process of transitioning from childhood to adulthood while experiencing the physical changes of puberty, and is conflated with adolescent. However, the developmental changes of adolescence, such as puberty (particularly in females) and the transition from primary to secondary school, typically begin around the preteens, while cognitive and physical maturation continue into the 20s. Thus, the teenage years only provide a very approximate age range of human adolescence.
Despite its commonality in everyday usage, teenager is a relatively modern introduction to the English language which debuted in print around the 1910s, and did not become popular until around the late 1940s and early 1950s as a marketing neologism.