Enlarged prostate, or benign prostatic hypertrophy (BPH), is a benign enlargement of the prostate gland that occurs in men as part of the normal aging process. BPH is not a cancer and does not itself have any bearing on a man's life expectancy.
Note in the above image that it is not the overall size of the prostate that can cause problems, but rather the extent to which it pushes on adjacent tissue:
a) inward upon the urethra, thereby blocking the flow of urine from the bladder.
b) upward toward the bladder, thereby irritating the nerves at the bladder opening.