I was talking about this idea with Claudio Fernandez-Araoz, senior advisor at Egon Zehnder International. He’s a globetrotting Argentinian–not a headhunter like most at the big search firm, but a go-to consultant on talent development. His 2007 book, Great People Decisions, is based on research on how the best developers of talent–Southwest Airlines , McKinsey, Intuit , Hewlett-Packard , and General Electric , among them–manage their high-potential people. These companies stretch their execs in all directions. And the execs learn not just multiple skills but also how to be flexible.

Fernandez-Araoz’s latest research involves “competency assessments” of executives in Japan–part of 6,000 or so talent assessments that Egon Zehnder conducts across the globe annually. To his surprise, Fernandez-Araoz told me, “In Japan, unlike in other countries, there’s a negative correlation between age and competency.” Japanese executives show higher-than-average potential early on, but later they tend to flag, according to Egon Zehnder’s research.

Actually, it’s not so surprising why “competency”–the firm’s measure of fitness for a job–declines as Japanese executives grow older. “Their potential is not being developed because they don’t switch jobs and companies and industries,” Fernandez-Araoz says, adding that in Japan’s age-based HR system, managers tend to get promoted for tenure, not competence. “This limits the development of the high-potentials, while lowering the overall level of competence.”

So go ahead, stretch yourself. And think about the four keys to successful leadership, according to Fernandez-Araoz: strategic orientation, results orientation, influence and collaboration, and team leadership. In today’s collaborative world–where success also rides on lifting confidence in all around you–team leadership, I’d guess, is most important of all of these.