The pearl that is cut in half showing the nacre thickness of the pearl from Port Stephens Australia is possible. When I worked for the company, Australian Radiata, we achieved about 1.5 mm of nacre cover in about 18 months given the right conditions and the correct farming practises.
The shell size for this seed was between 60 to 80 gram and was less than 2 years old when the seeding operation took place.