At first sight this seems a ridiculous idea, that has apparently been refuted by the great accumulation of knowledge through human history; but I believe there is a sense in which the broader argument is indicative of a profound insight - and this is why the argument has been taken seriously for more than 2000 years (ie. since Plato).
The sense is that life is two curves running from childhood to maturity - a rising line of self-consciousness which increases from childhood to a maximum plateau attained at adolescence. And a descending line of innate and spontaneous knowing which is high in childhood (albeit it is an unconscious knowing), and reaches a nadir in at adolescence.
In modern society adolescence is (spiritually) usually where matters stop - what we call adulthood is not 'maturity' but merely a sustained and degenerate adolescence. Modern 'adults' have lost their spontaneous natural knowledge (instead just passively absorbing propaganda and hypothesies from 'society') and they live in a cut-off state of self-consciousness (so cut-off that it doubts and denies even itself).
The task of adolescence ought-to-be to change that descending line of knowing into an arc - rising in adult maturity to reach the same kind of spontaneous and universal knowing that we began-with - but this time it is conscious knowing.
Thus, children know everything but are unaware of the fact, adolescents know nothing and are aware of the fact; but spiritually-mature grown-ups potentially know everything, and know-what-they-know.
I say adults potentially know everything, because the process of discovering-what-you-already-know is linear and happens in-time; so it would be more accurate to say that knowledge is un-bounded, open-ended, and tends-towards a situation of knowing everything-that-can-be-known - always from the perspective of a single self.
This scenario is, presumably, why all real learning - all knowing of truth - has the distinct feeling of being a realising, a remembering, a recognition... true knowledge is always 'familiar' - we always feel that we 'always knew that' but had never articulated it. I'm saying that we always Did know that - but did not realise we knew it, and could not use that knowing until after we had articulated it.
In terms of knowledge the trajectory is therefore from unconscious knowledge to conscious knowledge; from the implicit to the explicit; from immersion-in knowledge to standing outside it; from passivity through contemplation to creativity.
