It takes about 1 year for Panulirus cygnus to complete its entire larval cycle. During the larval cycle there are about 11 complex stages. At the end of a year, the juvenile rock lobsters are considered puerulus. In this puerulus stage, they are normally 25 millimeters long, and look like minature adult lobsters. In this stage they have an unusually low sensitivity to temperature changes, which works as an energy saving adaptation. In the puerulus stage they drift back to the coast and sink to the bottom where they stay for 2 or 3 years while they slowly mature. In this stage, the rock lobster could possibly grow 4 centimeters per year, which is very rapid. This rapid growth slows down as the lobster ages. The rock lobsters reach their full size at around 10 years of age.
Western rock lobsters must, like many crustaceans, shed their exoskeleton in order to grow. Molting occurs frequently in the younger ages, and approximately one or two times a year in maturing lobsters. The lobsters will hide for a few days after they molt because they have a new soft shell and are defenseless against predators. It is also a possibility that the lobsters may eat what they molt so they can retain the calcium in it to aid in forming their new shell.