A Cheddar’s sharpness is a reflection of its age, says Lynne Devereux of the California Milk Advisory Board. Most packaged supermarket cheeses start out slightly sweet, then take on a tang. Mild is aged only 2 months, medium 2 to 4 months, sharp 4 to 6 months, and extra-sharp about 1 year. The reverse holds true for Cheddars at specialty cheese counters, which start out sharp and develop a mellow, nutty flavor with time.