Construct the barrier two or more inches above the ground to encircle the stem. The barrier normally keeps cutworms from feeding. If needed a spray of diazinon or Sevin directed towards the base of the plant can also be used to protect the stems. Follow label instructions for the crops you plan to grow. No one really knows how tall nor how old a tree has to be to flower.
Trees do seem to have a reach a certain stage of maturity before the blossoms can form.
Most flowering golden rain trees are four to five years old and over fifteen feet tall. It appears you may have to wait another year or two for the yellow fall blossoms. It is vine-like and has small purple flowers. I think it may be creeping beggarweed. Spot killing beggarweed is the best way to eliminate it's strangle hold on St. Augustine lawns.