The amount of sleep and how it is distributed in terms of stages of NREM sleep and REM sleep changes over the course of our lives (Fig. 1).
The greatest amount of sleep can be observed in newborn babies. As the years go by there is a reduction in the amount of REM sleep, above all.

A regulating mechanism tends to keep the length and depth of sleep constant. In fact, sleep deprivation then leads to a catching up on lost sleep. Fig. 2 shows that this catching up manifests itself through an increase not only in the total daily duration of sleep and its NREM stages (in red) and REM stages (in black) shown on the time lines, but also in depth, seen in the intensification of low frequency waves on the electroencephalogram during NREM stages.

Fig. 2: Hours spent sleeping in normal conditions (Control) and after keeping the subject awake all night and all the next day (Catching up). Time spent in NREM sleep is shown in red, time spent in REM sleep in black.  The line shows the relative width of the low frequency waves of the EEG during the various stages of NREM sleep
(Credit: Amended from A.A.Borbely. Sleep homeostasis and models of sleep regulation. In "Principles and practice of sleep medicine". Saunders 1994)