British advertising giant WPP Plc sees potential in Japan’s shrinking market, with elderly consumers a segment to tap into, the head of its Japanese operations has said. Japan’s population is expected to continue to decline and age, reflecting its falling birthrate, but there is a chance to “further unlock opportunities,” said Kyoko Matsushita, who took the newly established post of CEO of WPP in Japan in April. “The good news is that older or aging, doesn’t mean you don’t consume things,” Matsushita said in a recent interview with Kyodo News. “You actually have more disposable income or savin…