How do you establish when a student is mature enough to deal with certain texts?

I think that teachers must slowely bring in texts and their maturity level. Starting out a certain level and working there way up, perhaps to build a students maturity. I also think it is important that teachers address the issue before assigning it and talking about it openly with the class. I feel that way the teacher can gauge the maturity level based on the students responses how they might handle the book or topic. Perhaps if the students dont handle the discussion in mature manner then maybe the students aren't ready to handle that particular subject. Maybe even before having an open discussion , the teacher could have the students write about a paritcular subject, expressing their ideas thoughts or beliefs which might give insight as to if they are mature enough or not. In my opinion, I feel after the ninth grade most students are capable of handling most topics. I say ninth grade because it seems that the transition from eighth to ninth grade is a pretty big one and in ninth grade students are keeping those immature values while learning to be a high schooler. They still can't handle some issues but are simultaneously learning how to deal with others. Yet, I also feel that some tenth graders can't handle some mature topics but that is also based on their background and what they have been taught growing up.