]It's not simple lack of experience, they are mentally immature. It's not a simple matter of telling them stuff. Their cognitive functions are still developing and while I'm no expert, I highly doubt a 4 year old is able to process what an academic truly does, much less want to be one, expect for if their parents want them to.
That is not true. My favorite author, J.R.R. Tolkien could read well by age 4 and he was educated by his mother, Mabel during his early years. I think many children are more immature than they used to be because we coddle them more and treat them like they are helpless. While it is true four year olds are still developing, they are quite capable of understanding more than people give them credit for. I think back in the old days, young children matured faster due to how harsh life was.
A good example is the manga, Barefot Gen, a story about the bombing of Hiroshima. Granted the protagonist was six years old, he was quite resourceful and mature for a little kid and took care of his mother and newborn sister. Although fictional, the story and events are real because the author lived through all of the events in the manga and was the same age as Gen.
Anyway, Gohan is part saiyan and appears very intelligent for his age, so it's very possible he could be studying difficult material.