By 2020, Millennials over the age of 25 will make up 19 percent of the U.S. population, and are expected to increase grocery spending by $50 billion dollars. How can you make sure your store has a piece of the Millennial pie? First, understand how this fickle demographic regards food, health and wellness.19% of the U.S. population by 202019% of the U.S. population by 2020