There are several things that could cause this issue, but I would say that it is likely one of two things. Either your mock orange's soil has too much nitrogen, or it is not getting enough sunlight. The fact that you said it's 5 years old leads me to believe that it is in a spot that isn't getting the best sunlight. The process of flowering is an expensive process for the plant and if the plant can't afford to do it, it will refrain. Plants will need a lot of energy to flower successfully, so if it can't get enough energy from the sun they may never flower. Have you tried using your EasyBloom to see the sunlight situation?