Yes, a 12 year old can absolutely sleep on the top bunk! In fact, many kids enjoy sleeping on the top bunk because it feels like a little fort or treehouse up high. Of course, there are a few things to keep in mind when your child is sleeping on the top bunk. First, make sure the mattress is secured tightly to the frame and there are no gaps where your child could potentially fall through. Second, it's a good idea to put a bed rail on the side of the bed closest to the wall to prevent your child from falling out. And finally, be sure to teach your child how to get down from the top bunk safely, in case of an emergency.