There isn’t a perfect answer here yet.  The pediatric items will likely work in this age range, but they haven’t yet been tested.  The pediatric items are targeted towards an 8-18 age range and some of the wording may feel a little “young”.  The adult items are appropriate for young adults, but then you are using two different measures in one sample.  The PROMIS network is conducting multiple studies that will link the pediatric and adult scales so that in the future it won’t matter which scale is used.  Review the banks of interest to determine what is best for your study.