Final answer:
The age that would be used in plotting the growth of an infant born at 30 weeks gestation is the actual age of the infant after birth.
Step-by-step explanation:
The age that would be used in plotting the growth of an infant born at 30 weeks gestation, assuming that 40 weeks is full term, would be the actual age of the infant after birth. Gestational age refers to the duration of the pregnancy, while actual age refers to the time elapsed since the infant was born. In this case, since the infant was born at 30 weeks gestation, their actual age would be the number of weeks that have passed since their birth.