When D.J. Vander Slik was mowing lawns in Grand Rapids, Mich., at age 12, a customer asked him for a receipt. He didn’t have any, so the homeowner helped him write something up, jotting down D.J.’s Lawn Service on the slip. “I thought, ‘Sure, that sounds good,’” Vander Slik says of his 12-year-old self. The […]