IN SCOTCH AISLES across the country, a reformation is quietly under way. Among the stolid contingent of age-emblazoned single-malts—the Glenlivet 12, the Macallan 15, Talisker 18—a mysterious new crowd is creeping in, and their labels are defiantly numeral-free.

For decades, the Scotch industry has marketed its single malts with the prominent use of age statements—that number on the bottle that, by law, represents the youngest whisky therein. Now, more and more distillers are omitting the information entirely from their...