I have had Hoya callistophylla for over 15 years and think it is one of my oldest Hoyas. It requires copious amounts of heat and humidity to flower, and since I have not had room for it in one of my grow tents for a very long time, I have not seen flowers. In the spring and early summer I finally chopped up my very large and road worn plant and sold off most of the cuttings. I kept the worst cuttings for myself and rooted a number of them. One of the brand new cuttings surprised me and actually bloomed. I was pretty surprised and happy.