Ask Mr. Smarty Plants

 Texas Mountain Laurel Sophora secundiflora (Texas mountain-laurel) is a hardy Texas native, and one of the reasons for growing it is to see and smell those gorgeous flowers. Flowering of course is part of the reproductive process and plants tend to do this on their own schedule providing other things are going well in their life. I haven't found anything about a specific age for flowering for the Mountain Laurel, but three years is the earliest age that was mentioned.

On the NPIN page for Mountain Laurel (see link above), you can find the growing conditions that are favorable for growth. Lets look at three that are often problematic

Light requirement: sun, Partial Shade, however the plant blooms more profusely in full sun.

Soil moisture: Moist, dry. Over watering can "drown" the plant at worst, and can inhibit blooming.

Soil description: Dry, rocky, well drained soils. Sandy, Sandy Loam, Medium Loam, and Clay Loam. This is tied in with soil moisture.

As to fertilization, the ratio of Nitrogen:Phosphorous that the plant receives can influence the flowerng process. Higher nitrogen can inhibit flowering. It is almost an article of faith at the Wildflower Center that you don't fertilize native plants. In the case of Mountain Laurel, it is a legume and is fixing its own nitrogen. If it is also getting high nitrogen from the lawn fertilizer, the balance is shifted toward non-blooming.(See previous answer)

Your Agri-Life Extension Service in Harris County can provide soil testing that will determine if any fertilization is needed.

This link provides good information about growing and caring for Mountain Laurel.