Q.I Have Cumquat Plant 16yrs No Flower No Fruit
Plant just grows tall not busyi trim top every 2-3 yrs. I live in CA USA zone 9A -9B

Certified GKH Gardening Expert
This could be an issue with soil fertility. Sometimes, lacking phosphorus and potassium will cause a lack of fruiting. Here are some articles that will help:
https://www.gardeningknowhow.com/garden-how-to/soil-fertilizers/testing-soil.htm
https://www.gardeningknowhow.com/garden-how-to/soil-fertilizers/soil-ph-plants.htm
https://www.gardeningknowhow.com/edible/fruits/kumquat/growing-kumquat-trees.htm