Dillard's declined to comment.
The lack of board turnover also means fewer seats can open up for women, who represent 19 percent of directors currently, or minorities, with just 15 percent at the S&P's largest 200 companies.
One company that has most famously benefited from veterans is Berkshire Hathaway Inc., which has five directors in their 80s and 90s -- including the 84-year-old Warren Buffett. Berkshire, which also has four directors in their 50s, produced total returns of 168 percent from 2004 to 2014.
The experience that comes with age sometimes trumps knowledge of new trends, said James Post, a professor at Boston University's School of Management.
"With age, you have accumulated wisdom," Post said. "And that's important to have in the boardroom, especially since we've just lived through such a turbulent time in business with the Great Recession.'"
The number of older and long-tenured directors is likely to grow as many companies limit their top executives to one outside directorship. With fewer working executives available to become directors, boards are relying on retired ones. More than half of new directors elected last year are retired senior executives and professionals, compared with 39 percent in 2009, according to Spencer Stuart.
With increasing numbers of directors in their 70s, "the time for succession planning is now," said Jamie Smith, assistant director of EY Center for Board Matters. "Given the data we're seeing, boards shouldn't delay doing this."