We have handled a lot of SR cases this year. Almost all have involved internet "hook ups" in which the child lies about their age. That is a defense to SR. You need to talk to an arty about possible defenses. Can't tell you how much time you are facing without info on any prior felony record you might have.
The ages of the victim and the defendant is important in grading the offense. Most cases I have seen are charged as a B felony. This link will show you the ranges of punishment: http://collinsfirmtn.com/learn-more/blog/tennessee-sentencing-guidelines
The aggravating factor in the charge will depend on the age of the victim and the defendant and they gap between. An additional factor is if the defendant was in an authority figure position over the victim. That could be any where from a babysitter to a Teacher.