In other words, national age is a Goldilocks problem. Country populations shouldn't be too old, and they shouldn't be too young. To avoid demographic problems, a country's age needs to be just right.* Off topic, but still relating to language, a heard a recent radio account for someone who had determined (it doesn't really deserve to be called a "study"; a pre-existing online calculator was used) the reading level of the lyrics for 225 recent number one Billboard hit songs (that were at number one for at least three weeks) by band and by genre using software applying standard reading level tests.
The most sophisticated song had a reading level of 5.5 (Red Hot Chili Peppers’ “Dani California”) (readable by a mid-year fifth grader); the most sophisticated artist was at grade level 3.95 (readable at the level of a third grader at the end of the academic year). The most sophisticated lyrics by genre was country music which was in the low 3rd grade level. Some hits (e.g. Three Day's Grace's "The Good Life") were below the first grade level.
By comparison, Charlotte's Web has a reading level of 4.4, an ordinary daily newspaper is typically written at a 5th grade reading level, the first Lemony Snicket book ("The Bad Beginning") has a reading level of 6.4, and the standard for "functional literacy" which is also often used as a standard "floor" for people who want to set a rigorous reading level standard for high school graduates, is frequently set at the 9th grade reading level, about the same reading level of George Orwell's book "1984" which is reading level 8.9. Jules Verne's 20,000 Leagues Under The Sea has a reading level of 10.0. An unabridged translation of "Don Quixote, by Miguel de Cervantes Saavedra has a reading level of 13.2. (All references to reading levels for books from here).
For what it is worth, I think that this is mostly a function of reading level tools that are insufficiently sophisticated themselves to accurately measure the reading difficulty of poetry (which is what music lyrics are), because these metrics place undue weight on factors like short sentences, insufficient weight (for poetry) on word difficulty, and typically no weight on subtle factors like the use of metaphor, double meaning, and references to experiences that children may lack. After all, the average song ranged from an average of 250 to a bit less than 700 words each by genre (rock has the least; R&B and Hip Hop which includes rap, has the most), so there isn't much room for long sentences by the virtue of the lyric form.
The Flesch-Kincaid readability level score, for example, depends entirely upon the average number of words per sentence and the average number of syllables per word in a piece, which may be correlated with readability in ordinary prose, but is a poor instrument for measuring the sophistication of music lyrics. (The song "Supercalifragilisticexpialidocious" from the musical Mary Poppins, in contrast, would by treated as profoundly sophisticated by this measure (9.1), since a large share of the words in the song have fifteen syllables.)
Of course, another factor dumbing down the analysis is the focus on number one hits, which by definition must be accessible to maximally large audiences. Songs with smarter or more difficult lyrics, like art movies relative to blockbuster movies, tend to have smaller audiences.
This 653 word blog post has a reading level of 10.3. Yesterday's renewable energy post had a reading level of 13.2.