The Answer Varies with Age
Sleep needs vary from person to person, and they change throughout the life cycle. Most adults need 7 to 8 hours of sleep each night. Newborns, on the other hand, sleep between 16 and 18 hours a day, and children in preschool sleep between 11 and 12 hours a day. School-aged children and teens need at least 10 hours of sleep each night.
Some people believe that adults need less sleep as they get older. But there is no evidence to show that older people can get by with less sleep than younger people. As people age, however, they often get less sleep or they tend to spend less time in the deep, restful stage of sleep. Older people are also more easily awakened.
Does it really matter if you get enough sleep? Absolutely. Not only does the quantity of your sleep matter, but the quality of your sleep is important as well. People whose sleep is frequently interrupted or cut short might not get enough of certain stages of sleep. In other words, how well rested you are and how well you function the next day depend on your total sleep time and how much of the various stages of sleep you get each night.
— Sources: National Institutes of Health