There are also two metabolic reasons for increased sleep time urinary increase, besides the aging common ones we think of in older patients-- prostate, or overactive bladder etc.

1) if your blood pressure is high during the day, and goes down when you sleep (or if you take your BP meds at night), increased urine flow occurs. This is because when you are up and moving around during the day and have higher blood pressure, the renal arteries clamp down to save blood flow so it can be diverted to the brain and muscles. Once you suspend activity and lie down, these arteries open back up and urine flow begins again.
This can be a sign of edema during the day also. People with enlarged hearts also can make more urine at night.

2) If you eat a large meal for dinner, and are insulin resistant or beginning Type II diabetes, there will be more urine at night also.

In general getting up once in the night for older patients is considered normal. More than once is a signal that something is possibly wrong. For males, prostate issues I think are the most common, non metabolic cause.