The prostate is part of a man’s sex organs. It is the size of a walnut and surrounds the urethra. As the prostate grows larger it can press on the urethra. This narrows the urethra and can cause some men with prostate enlargement to have problems urinating. Prostate enlargement is said to be the most common health problem in men older than 60 years of age. The prostate usually starts to enlarge at about the age of 40.