The privilege page states that the question must be at least a day old. However the screen shot indicates that the question is more than a day old so it should be there.
I've noticed that your rep is exactly 15,000. Perhaps there's a bug in that the privilege itself checks for rep > 15000 while the notification checks for rep >= 15000.
Most of the time you'd be over the limit rather than on the limit so you wouldn't notice the error.