I am only twenty, I had finished Kant's critiques by the age of sixteen, I have since become a Theological Scotist, so what exactly is there that I don't... Get?
I mean, it's not like philosophy or metaphysics is particularily stimulating or challenging, the notions in it are rather simple.
Nb: I am willing to recant if you can somehow demonstrate that there is a particular concept or theorem within metaphysics or ethics that I am unable to understand.
A) Plato's public matters or, "republic" may make such a referance, but it does not indicate in any way maturation for me to go to a library or browze the internet to find it. I could ask you which synoptic author writes about Socrates swinging in a basket in the thinkery, and on what page he measures boots for fleas, but that would prove nothing.
B) It is possible that people gain experience and understanding, which allows the apt contextualisation of new and old concepts; nonetheless, if one is to contend this then one must presume the unatainability of a state of maturation or "optimal" understanding, elsewise, even old people would not atain this, as they are still encountering new experiences; and if we are to posit that there is a subjective or individual optimal understanding then to presume that it is even significantly based upon age instead of experience and contemplation is foolish. - If, like you assert: it is "folly" for one to believe that ideas and opinions cannot change, then you also must accept that even older people are subject to this, and thus; cannot be said to be objectivelly matured, only further in maturing to an ultimatly unatainable end.