The Lau triplets were the foremost scientists in the field of optimizing the human body to better the earth. After an experiment went awry the women were left with super fit physiques and the need for a new purpose in life. Each sister took on a new career that would employ their newfound physical prowess.
It is implied that the triplets were scientists, becoming fit after an experiment gone awry. This may imply that they were employed in the Science career before.
Despite the sisters being triplets, their age do not actually match. Mai is the oldest with 13 days left in her stage, Annie with 18, and Lucy with 19. This may be an unintended mistake by the developers.