The order in which different brain areas reach maturity must be crucial to how activity-guided development creates functional specialisation (there’s good stuff on this in Rethinking Innateness). Here’s a maturational timetable (via) for different brain areas:
Notice that it’s areas associated with audition that finish myelination first (in the womb), and the neocortex which finishes last (about 25 years later).
Ref:
Elman, J., Bates, E., Johnson, M., Karmiloff-Smith, A., Parisi, D., & Plunkett, K. (1996). Rethinking innateness: A connectionist perspective on development. Cambridge, MA: MIT Press/Bradford Books.