My guess would be the soul was wiped clean during the insertion process, and therefore everything needed to be learned anew. Otherwise he would have been fluent at birth. And I dont think that was the case.
Study John the Baptist, his life, his family;
Study Jesus as 12-year-old (became adult legally); think of Jesus later reading the Scripture in the Synagog;
Study the Essenes, especially at Qumran... Why were they preserving those ancient copies of Scripture?
The Essenes were founded by a Teacher of Righteousness; he wrote that after a time there would be a new Teacher of Righteousness.
John the Baptist?