Why isn't my bougainvillea flowering?

Why is my 4-month-old bougainvillea not flowering? It's growing well with plenty of sunlight and regular watering, but there are no blooms. I've been careful not to overwater, and it's planted in well-drained pot. Could it be too young to flower, or is there something else I should be doing to encourage blooming?

 

Too young to flower. Give it a few years.

 

Thanks Michael, but when I purchased them they were having flowering.