I actually noticed that part. It was the grammar that I didn’t get which you have helped with. Thank you very much. My wife says this language is not in common use and that if I heard it, it would probably be in a period drama (時代劇). She wasn’t here when I posted the original question but I think your explanation is probably clearer than what she would have provided.
You don’t have to go so far back. The professor in 時をかける少女 that we just finished reading in the beginner book club talks like that. That book was written in the 60s.
I have read the first 2 or 3 volumes of Yotsuba a long time ago.
Mmm, it’s hard to say. Yotsuba has a lot of broken grammar and slang, but, as a manga, gets a lot of visual cue. 時をかける少女 isn’t bad in terms of grammar and vocab, but still, it’s a book, and a bit dated at that. The way people talk feels a bit stiff nowadays, which can also be a challenge, depending on your background.
I think the best is to look at the sample pages (accessible from the home thread of the book if I remember correctly) and check for yourself.