I (precocious, pretentious me) read Anna Karenina in 7th grade. It was long but not difficult. Keeping track of the characters was the hardest part.
I’d like to say the story stayed with me, but alas it was the reaction of adults to my reading matter that I remember.
Part of growing up was realizing that being precocious really isn’t a thing anymore at some point.
This resonates with me very much. I remember being very proud of myself each time I was tested in school and I was told I was reading at such-and-such a grade level above my own. Now in my 30s, I still like reading a lot, but there's so much more to reading than finishing books.
I still have a bit of reticence toward admitting that I find some books hard or haven't finished them. I found the Iliad enthralling and the Odyssey very good, but basically any other English epic poetry or drama is such a grind and I've given up many times.
I think a lot of the deeper enjoyment of literature comes when one has a sufficient understanding of the relevant culture & context and can adequately bring the characters to life. I studied Latin for 5 years (and Spanish for 3, Portuguese for 2 and German for 1), and I can tell you the immersion into Roman (and Roman Empire) culture absolutely made reading everything from Homer to Herodotus to Augustine to Seutonius to Cicero, Catullus or Ovid far more engaging than if I'd picked up any of these authors without context.
I recently started reading Anna Karenina, and even for me as an adult, there's a lot of people with a lot of interconnected relationships to keep track of. But I am surprised by how moving I find it - I guess I expected it to be more distant somehow, but the people really spring to life. If I'd read it as a kid, I imagine I would be relating differently to all of these very adult concerns.
One of the best gifts I ever got was when my dad plopped down a big box full of old classical adventure novels (Twenty Thousand Leagues Under the Seas, King Solomon's Mines, Captains Courageous, Three Musketeers, Count of Monte Cristo type of stuff) and I devoured all of them over the course of the next year or so. I'm sure I would appreciate a lot of different things about them if I read them now, but they certainly held up in terms of being engaging in spite of them all being 100+ years old by the time I got my hands on them.
I was a precocious reading kid too, and I sometimes wonder how much I understood of all the stuff I read. I feel like I remember it decently enough, but there must have been a lot going over my head.
This made me smile because I did exactly the same thing (i.e. I also read Anna Karenina in 7th grade, and was very pretentious). I mostly read during lunch periods when it probably would have been a better idea to be developing my social skills.
I remember being most interested in Konstantin Levin's efforts to modernize his farm estate.
I think that at the time I thought that I understood the difficult books that I was reading fully, but looking back on it I must have missed so much. I'll need to have a re-read one of these days.