I'm of the opinion that Old Spock overwrote "baby" Spock and that therefore baby Spock did not get a chance to develop. Despite every indication that he could, with retraining. And "his mind's a void" doesn't explain that he could howl, would take comfort from Saavik (of any kind), walk (which requires years of muscular development)... etc. IMHO had the Katra not been involved the Vulcans would take him in and educate him presumably to a functional adult.
Very much like "Sim" in Enterprise.
Very much like "Sim" in Enterprise.