Of course books that do stretch one’s boundaries may be instructive, or really, demonstrably beneficial, even if they’re not on some college reading list! Of course that isn’t strictly tied to age (though there will be a certain correlation).

I just mean that most adult fiction reading is adults reading YA because they want something easy that they don’t need to think much while reading, that doesn’t challenge them, often to the point of being written in the first person because it’s harder to track context in 3rd, and harder to orient oneself within a 3rd person narrative voice (not to overstate the difficulty, but it does require closer attention and asks more of the reader—and I’m not joking or pulling this out of no-where, ask some readers, ask some editors, ask some agents, enough of the market considers 3rd too hard to read and will skip books that aren’t in 1st, it’s a real consideration in planning a book). Or reading bodice-rippers literally written from a template (you don’t put out five novels a year without some effort toward developing efficiency). Or re-reading their favorite Harry Potter book for the sixth time.

What would I suggest instead? Anything else that’s not very challenging and passes the time pleasurably! Watch a reality show or whatever. The latest Netflix drama. Play some Super Mario Bros. These folks aren’t working their way up to “better” literature, they’re just having a good time. Which is ok!

Again, it’s not a problem that the activity is low-value if that’s what someone wants. It’s fine and normal to want easy entertainment, at least sometimes. Lots of adults read exclusively or almost-exclusively for that kind of low-effort entertainment, and that is OK. They don’t need to replace it with reading War and Peace or doing calculus problem sets or something. Those are probably “better” activities if your goal is improvement, assuming you’re ready for those kind of things. But that doesn’t need to be your goal, and it’s ok if that’s not what someone’s looking for in the books they read.

According to what sells, most people just want an easy story with few or no words they hadn’t learned by junior high, and a narrative that’s clear and leaves little to inference (and certainly doesn’t rely on it!) They want short sentences, that don’t force them to keep much context on their head.

They aren’t working their way up to works that might stretch their abilities, they’re looking for books comfortably within their existing abilities. And that is OK. But the notion that reading may take place that’s about as low-value as trash TV, and that that’s probably the majority of adult reading, seems to bother some enough that they want to paint reading as per se virtuous, valuable, et c. Meanwhile, it’s not any more so than listening to music is. Two people listen to several thousand hours of music, one comes out the other end able to hum Mmm Bop by Hansen, and that’s about the extent of what they took away; the other is familiar with the song and can also tell you how its rhythm is connected to Senegalese folk music and the harmonies reminiscent of early French polyphonic choral hymns. The music-listening wasn’t per se equally valuable from the widening-one’s-horizon perspective, but both may have enjoyed themselves. What’s weird is deciding to plaster “MUSIC LISTENER” on your tote bag as if that by itself means anything—for either of these subjects, really.

That so many folks end up with a fairly low reading level, as adults, is telling: if they remain readers regardless, as many do, they’re probably avoiding works that might force them to get better at it, or else surely they’d markedly improve over decades. I don’t think it’s a coincidence that most folks also stop getting much better at math around 7th or 8th grade, it’s just that for whatever reason we see admitting that as Ok and admitting to being a poor reader as nearly unthinkable. I think that’s about the time both get really uncomfortable for a lot of kids, and they realize they can just stop and skate by on what they have, and they’re not really wrong. I don’t think most of them who nonetheless enjoy reading are working toward tougher books any more than I think someone who likes sudoku puzzles is working toward solving PDEs. And that’s fine.