There is a big difference between the amount of hours of sleep you can get by on and the amount you need to function optimally. According to the National Institutes of Health, the average adult sleeps less than seven hours per night. In today’s fast-paced society, six or seven hours of sleep may sound pretty good. In reality, though, it’s a recipe for chronic sleep deprivation.
It really depends on age
Most adults need seven to nine hours of sleep per night, but the amount varies by person and age. Seniors generally need an hour or so less than younger adults; teens, children and babies require up to several hours more. To determine how much sleep you need, find a time when you are able to fall asleep within half an hour and then wake up without an alarm clock the next morning feeling refreshed. Add up the hours you slept.
Aging and sleep
Along with the physical changes that occur as we get older, changes to our sleep patterns are a part of the normal aging process. As people age they tend to have a harder time falling asleep and more trouble staying asleep than when they were younger.
After age 65, you will likely need between seven and eight hours nightly. And since older adults often have trouble sleeping this long at night, daytime naps can help fill in the gap.
Source: National Institute of Health