The assumption that your teen years are the best, most shining and radiant part of your life—and that as soon as you reach legal majority you become a decaying thing that can only crawl in the rotting morass of adulthood all the way to your death—is very much a common Japanese idea... but it isn't at all a Western idea; more like the opposite, in fact. I'm surprised nobody felt offended by this strip and reacted with anger.
I guess we've all already been mentally colonized by the Japanese. :P Come to think of it, I haven't read any rants against lolicon manga in a long time...
I think it's pretty common in the West as well, although it also includes college. There is pushback for it, but there are plenty of media that talk about the high school/college years as "the best years of your lives".
But you gotta admit that the angsty tormented teenager trapped between childhood and adulthood is far more frequent in Western literature.
But it's not a trope used to depict teenaged characters, it's a "middle-aged person romanticizing youth" trope.
(Although to be fair, the "next we're going to be third-years and have to decide what to do with our lives and then get jobs, etc., so let's make fun memories while we're footloose and fancy free" trope shows up in manga pretty regularly, too.)