>>283572047
This isn't even a matter of being underage, it's just a matter of being informed. Anne was one of the first English language novels translated into Japanese after the war, and multiple generations of children grew up reading it. There used to be a "Canadian World" theme park in Ashibetsu, Hokkaido, with a replica of the Green Gables home and park staff would cosplay as Anne and Gilbert. Excerpts from the books and from scripts for adaptations are used in English textbooks and exams. Canada has hundreds of thousands of Japanese tourists every year, and Prince Edward Island in particular really relies on travelers from Japan to prop up its economy. Couples fly to PEI to get married.
Couples.
From Japan.
Fly to Prince Edward Island
(halfway around the world)
To get married.
I can't actually think of a fitting analogy for an English country. There isn't any one book that's as pervasive and enduring. Maybe Harry Potter, but even that's died out and Anne is still popular 130 years after it was first published.
Anne is also the reason you have red-haired tsunderes as well as Studio Ghibli.