I’m currently reading 銀河鉄道の夜, and it’s challenging for a couple reasons. I’ll start by saying that the old fashioned language isn’t a huge issue. It’s funny seeing a kid say けれども when speaking to his mother for example, but it doesn’t really impact the difficulty. There are also occasionally words that use weird kanji, but in all those cases there’s furigana. So again, not a problem.
Overall there are two actual issues, both of which have little to do with the book being old. First, there’s way too little kanji use. It’s like I’m back reading kids books (I have no idea of the original target audience for this). I often find myself misparsing long strings of hiragana and having to reread, or otherwise pausing briefly to try to remember a word by the sound since I don’t have the kanji for reference. The second issue is that there’s a ton of specialized words. A lot of plant names, which I wouldn’t even know in English. And of course, all the constellations, which I also don’t know in English. In retrospect, not the smartest move reading a book like this when I don’t understand any of the constellation references.
In any case, it’s a really short book (which is why I picked it since I wanted to squeeze something in before かがみの孤城), so I’m going to power through. I’m about a third of the way through. It’s been a bit slow so far, but hopefully it picks up soon.