"Young adult" in this context is a publishing industry marketing tactic. It doesn't refer to actual adults. The target audience is mostly children who want to feel like they're getting away with something they're not supposed to.
Young adult literature is not "books for target range of 11-15". OP made that claim up to make it sound terrible that people who finished high school report liking to read books literally written for their age bracket. Official young adult age range is 13-18, which means literally high schoolers. And yes, they are already grown a lot, so those books frequently end up being popular among reading adults too.
I am from generation that read a lot. Huge bulk of what people, both adults and teenagers, read was something called "junk literature". It is fascinating how the "kids don't read for pleasure" panic instantly jumps into "it is horrible that when kids read for pleasure, they report liking books that are age appropriate and written so that their generation likes them".
I remember plenty of "young adult" books in the school library in elementary and middle school in the 90s. e.g. I read A Wrinkle in Time in 4th grade, and The Giver was assigned in 7th. I think Hatchet may have been a choice of assigned reading in 5th. IIRC (and a quick search confirms) all of these were marketed as young adult. I've always thought of YA as targeted at roughly 9-12 years old. I remember thinking the term was patronizing when I was a kid.
You seem to assume that reading fiction is some kind of competition. You read it as 9 years old, therefore it is shameful to read it as teenager or adult. That is genuinely absurd.
I never said a kid should not be allowed to read books outside of their demographic bracket. Kids can read books "officially" for younger kids, older kids or adults assuming it does not contain genuinely 18+ content. A kid reading book meant for young adults will typically miss some themes, topics or relationships. It will relate characters differently, will miss some motivation and some stuff flies over their head. I personally missed most of the sex in Witcher when I read it the first time when I was too young to figure them out. I thought some characters are just mean when adult me understood exactly why they do what they do.
Young adult category is not meant or written for 9-12 years crowd. That does not mean kids brain will melt. My own kids have seen and enjoyed entertainment meant for older people - but it was super apparent a lot of it went right over their heads when I talked with them.
I don't view it as a competition. I've never been big on fiction in the first place. I'm just listing books I remember being present if not assigned in classrooms when I was that old, and I remember these things being characterized as Young Adult, which struck me as condescending as a 10 year old.
By contrast, in high school we were assigned books like Brave New World, which makes a lot more sense as a book for that age range and is more what I'd think "young adult" should mean.
It will rot your mind! It will make your eyes square! Stop doing something that I am not doing!
> "junk literature" ... fascinating ... panic
Yes. It's funny how old this meme is. It's about as old as novels, at least. It's fun reading centuries-old novels and finding references (well, thinly veiled protests) to the holier than thou impeccable paragons of virtue that have nothing better to do than hassle someone who wishes to read a book.
I suppose there's been some progress, if the fiction police have had to retreat to a limited subset of fiction to call sinful.
I am from generation that read a lot. Huge bulk of what people, both adults and teenagers, read was something called "junk literature". It is fascinating how the "kids don't read for pleasure" panic instantly jumps into "it is horrible that when kids read for pleasure, they report liking books that are age appropriate and written so that their generation likes them".