The use of "teen" to refer to these ages is a relatively recent phenomenon. It first appeared in the early 20th century, likely influenced by the growing recognition of adolescence as a distinct life stage.
Here's how it likely happened:
1. Numbers ending in "teen": Numbers like thirteen, fourteen, etc., already had the "-teen" suffix, which naturally emphasized the "teen" part.
2. New social phenomenon: The emergence of "adolescence" as a recognized social stage created a need for a term to refer to this age group.
3. Shortening and combination: The "-teen" suffix became associated with the age group, leading to the shortening of "thirteen" to "teen" and the combination with "ager" to form "teenager".
So, the word "teen" wasn't invented as a separate word but rather emerged as a shortened and repurposed element from existing numbers, reflecting the social shift towards recognizing adolescence as a distinct life stage.