SEATTLE—About 35 percent of the 29,645 machinists in Boeing’s Seattle industrial hub are 55 or older.

A persistent theme in the business press is the presence of a skills gap in America. Thousands of U.S. manufacturing jobs are unfilled because there are simply not enough qualified workers.

Workforce diversity, both in leadership and the rank-and-file, is one of those ideals to which companies aspire without needing a true “business” reason.