Expiration date. The OED’s first citation is from 1963, while the first metaphorical use is a Daily Telegraph headline (OED calls it a “heading”) from 1987: “Socialism: the package that’s passed its sell-by date.” Sell-by date is not only more precise than expiration date but also is more mellifluous. Hence its appeal for now-inescapable and wearisome metaphorical applications. (Of the last 20 uses in the New York Times, only five refer to foodstuffs and fifteen to people, ideas, etc.) Google Ngram.
Ms. [Kathleen Hall] Jamieson’s list of double binds is a little past its sell-by date.(New York Times, April 2, 1995) /And the hippie-with-an-expired-sell-by-date look suits him [Paul Rudd] well. (Entertainment Weekly, January 24, 2011)
notoneoffbritishisms.com 
But would a Brit not call this an “expiry” date? (That one stopped me cold the first time I ran into it.)
That’s a new one on me. I will investigate–thanks.
As a native Brit, “expiry dates” usually refer to credit and debit cards, while “expiration dates” sound like an Americanism that we’d understand for anything of “limited shelf-life”, metaphorically or literally and would be accepted easily in an American TV show on our screens.
In Britain/E.U., “Sell By” dates have officially been removed from food products which now feature either “Use By” dates (as in, “this may make you ill if eaten after 19 MAY”) or “Best Before”/”Best Before End” dates/months for products that go stale or deteriorate rather than harbour potentially harmful bacteria. Additionally, “Display Until” dates are sometimes printed for stock control purposes at the supermarket or catering wholesaler and precede the Use By or Best Before date.
People still interchange “Sell By” dates for any of the above colloquially, and the metaphorical use is widely used for dated ideas, dated fashions etc. and probably appears more often than the literal sense in print nowadays. I agree that Sell By Date and for that matter Shelf Life are pleasingly mellifluous.