senior momentnoun [ C, usually singular ]
uk/ˌsiː.ni.ə ˈməʊ.mənt//ˌsiː.njɚ ˈmoʊ.mənt/informalan occasion when someone forgets something in a way that is thought to be typical of older people:
Is this just a senior moment or am I losing my memory?
I always write important names down, in case I have a senior moment.