the greying of something
From Longman Dictionary of Contemporary Englishthe greying of somethingthe greying of somethingthe situation in which the average age of a population increases, so that there are more old people than there were in the past the graying of classical music audiences → greyingExamples from the Corpusthe greying of something• Jacob, trim in his dinner-jacket, his dark eyes sparkling darker against the greying of his thick hair.