This reminds me of something. Just before my 20th birthday, a Venezuelan friend and I had a little discussion about the concept of "teenagers." I had lamented that my teen years were about to be over, since I was tying the word to numbers that ended in -teen. However, his idea of "teenager" was "adolescent" (Spanish adolescente) which wouldn't apply to a 19 year old.

The Spanish language doesn't have an equivalent "-teen" suffix. The closest term is "diez y ..." (ten and ...) which describes numbers from 16 (diez y seis) to 19 (diez y nueve). Adolescence for most people starts before age 16, so tying the concept to the "diez y ..." ages doesn't make sense.

In other words, despite every translator and teacher saying so, teenager ≠ adolescente. They each approximate the same life stage, and can at times refer to the same ages, but "teens" are a specific concept based on the English-language number system. It's just one of those linguistic quirks to look out for.