Parmesan is generally aged from one to three years, with the flavor becoming sharper and more pronounced over time. Its texture also becomes drier and more crumbly. Parmigiano-Reggiano fresco is aged for less than 18 months, vecchio is aged for 18 to 24 months, and stravecchio is aged for 24 to 36 months.  

Older Parmesans are known for their granular “bite,” which imparts a stronger, more pronounced (and prized) flavor than their milder, younger counterparts.  It’s no surprise that aged Parmesans are more expensive.