Teenage years, teenagehood, teenagers are western concepts. The term or its equivalent does not exist in
Asia culture(s) or anywhere else really. You are either old enough or not. In most Asian cultures one can be an adult from 12-
14 and official an adult from 15 upwards. Even in Native
America, the concept of a "quinceanera".
Teen was original based off of the number 10 (ten). Hence, the numbers ending in -teen are all in tens. Originally
people used to say "They are in their tens", just like "twenties, thirties, etc."
In more recent times the teen concept was created by the west, disregarding the original "tens" and replacing it with "teen" (based off the same etymology but definition has changed to refer to numbers ending in -teen).
Get your shit
straight. We can say early tens, mid-tens, late tens too. What's wrong with you?