That's because our ability to sleep for long periods of time and to get into the deep restful stages of sleep decreases with age.
(That; 's; because our ability to sleep for long periods of time and to get into the deep restful stages of sleep decreases with age) (our ability to sleep for long periods of time and to get into the deep restful stages of sleep; decreases; with age)
That our ability to sleep for long periods of time and to get into the deep restful stages of sleep
's decreases
because our ability to sleep for long periods of time and to get into the deep restful stages of sleep decreases with age
with age