The prostate is a small gland in men that is part of the reproductive system. It's about the shape and size of a walnut. The prostate rests below the bladder and in front of the rectum. It surrounds part of the urethra, the tube that carries urine from the bladder. The prostate helps make semen, which carries sperm from the testicles when a man ejaculates. As a man ages, the prostate can grow larger. When a man reaches the age of 40, the prostate gland might have increased from the size of a walnut to that of an apricot. By the time he reaches the age of 60, it might be the size of a lemon. Because it surrounds part of the urethra, the enlarged prostate can squeeze the urethra. This causes problems in the passing of urine. Typically, these problems passing urine don't occur in men until they are age 50 or older. They can, though, occur earlier.