It's not completely understood why some people have HBP while others may not.
This information is from the American Heart Association:
High blood pressure results from a recognizable underlying problem. This is called secondary hypertension. Some possible causes are a kidney abnormality, tumor of the adrenal gland or congenital defect of the aorta. When the root cause is corrected, blood pressure usually returns to normal. You may want to see an endocrinologist which do specialize in BP as well. In the mean time here are a couple of excellent sites you may want to read over as well.
read here (there are additional links on the left as well with great information)
read here (this site talks about teenagers with HBP)
Hope this helps, If you need anything else please feel free to ask. If you found this helpful don’t forget to click the *accept* button!