Age Appropriate -- who says, why, when, how?

A few days ago I posted a query to You All asking for suggestions for a reader, turning 12, who would like something to read as she finishes the Twilight series. I noted that I had some specific requests, such as no graphic sex or strong violence and no deeply Fraught issues that I personally would consider more appropriate for an older teen reader.

cristalia commented: N.B., my inherent bias in this situation is a concern that anything the reader considers too young for her or an effort to ...