Book related, but not quite

I've spent most of this year reading NA-books hoping to find something that really sticks out in both content and quality. So far I've come across more bad than good. (I'll probably give up on the genre for a while, because all the unnecessary drama is making me want to see a therapist.) However, there are two things I'm curious of regarding the genre in itself (and they're both very related to each other). I might do a post on the other topic later this week, but I'll start with this one:


The 17/18+ age limit on the readers of New Adult books.


Many blurbs of books in this genre have a warning about sexual situations, strong language, and similar content. After these warnings, they often state that the book is for readers 17/18+. The same goes for some reviewers (for instance on GoodReads). They also state, in their profile, that you should be 17/18+ to follow their reviews/befriend them due to the content in their reviews regarding these New Adult books.


Based on this, I'll assume/generalize that people don't want or think it's acceptable for people under 17/18 to read books which contain sexual activities on a larger scale.


Now, on a not unrelated subject, I'd like to talk about something I've noticed. In my school library, where youths from the age of 13/14 can lend books, there are a number of books that should be classified for 17/18+. For example, Fifty Shades of Grey. Yes, in my school library people as young as 13 can lend this book, among others, and these are classified as adult. However, would not rise an eyebrow if I saw someone that young read these books with sexual content, but I asked those working in the library if they would let them lend these books, and yes, yes they are allowed to do so. 


Before someone thinks I'm crazy for not lifting an eyebrow at a 13 year old girl/boy read a book containing sex. I would probably be horrified if someone that young read Fifty Shades of Grey, but more due to the unhealthy portrayal rather than sexual content. But them reading about sex, or even erotica? I wouldn't really mind. This is because, as someone who was 13 not that long ago, I know they talk more about sex and drugs than I do with my peers (17-18 years old most of us).


The age group which New Adult books are directed to (17-25) aren't that interested in sex as it's described. Because in reality, we care more about other things, such as studies/career and the future. However, those who are interested and talking about sex are those under the "appropriate" age group. So I'm quite curious about this 17/18+ limit. To me, I couldn't care less if a 13/14 year old read these books, because they come across these topics in daily life anyway. I understand that people might not want young people reading books with such content since they want to shield them from the topic for a while longer.


Now, to the real point: It would be interesting to hear your thoughts on this. Should young people be reading New Adult books even if they're under 17? Should there be another "age limit", and if so, at which age? Again, it'd be interesting to get other people's views on this, all opinions are welcomed and appreciated.