Why 7 years is the maximum cultivation time for freshwater pearls？

There are two reasons:

1. The pearl stops growing after 7 years. The longer the pearl is farmed, the less the oyster grows, just like a person. A person's height reaches 1.7 meters at the age of 20, but cannot reach 2.7 meters at the age of 30.
2. After seven years, the pearl will grow to the edge of the oyster shell, and its mantle will rupture, turning the pearl into a worthless bead without any luster, a dull and broken pearl. So no oyster farmer would risk cultivating pearls for more than 7 years.