Like most other adults, seniors usually need about seven to nine hours of sleep, though they may have a harder time getting it in a single block of time. But healthy older people are less affected by sleep deprivation than younger people. In one 2009 study, healthy people aged 65 to 76 had faster reaction times, focused better, and dozed off less than people 18 to 29 years old when they went 26 hours without sleep. Whatever your age, lack of sleep -- even one night -- can cause you to be irritable and vulnerable to stress. It can affect your memory and your judgment, too.