Final answer:
The autonomic nervous system begins development during fetal growth with myelination of spinal axons starting around weeks 21-30, but it is not fully matured until adolescence. There is no single gestational age at which the ANS is fully developed, as the process continues post-birth and is completed during the adolescent years.
Step-by-step explanation:
The autonomic nervous system (ANS) matures over time, starting from fetal development and continuing into adolescence. During developmental weeks 21-30, the fetus experiences rapid weight gain and the axons of the spinal cord begin to be myelinated, contributing to the initial development of the nervous system. However, the process of myelination, which is crucial for the efficient functioning of the nervous system, is not completed until adolescence.
Aside from the ANS, other body systems also undergo significant development during the adolescent growth spurt, with substantial changes in the prefrontal cortex, a part of the brain associated with executive functions. Therefore, the completion of ANS development is typically associated with the end of adolescence, although there is no specific 'fully developed' gestational age, as maturation continues post-birth and is influenced by various biological and environmental factors.