Noble demons are able to live long years by resting.  The higher the rank, the longer they need to Sleep, higher Demons/Angels rest up to a hundred years at a time (likely between several hundred year intervals of being awake).
Demons prolong their lives by Sleeping - put power shifts when one is Asleep, and that demon may even be replaced while (s)he is sleeping. One's power and influence over the lands can be transferred frequently, that's why the higher ranking a demon is the more they obtain safety nets.
It's been said that individuals have cycles of Sleep.
If one postpones their Rest, it results in their weakening, making them easy targets (as was the case with Baphomet), and eventually they start to fade (as is the current case with Michael).
There were also cases of some Sleeping for longer than usual. Dantalion is said to have Slept for a thousand years, and Metatron admitted to Sleeping for a long time.
Having (and making, via turning a human) Household Members is said to shorten the time one remains awake, and make them Sleep earlier.