Taking ἀκμὴ as the key term for understanding the Greek meaning of maturity, I depict the notion of “intellectual maturity” within the account provided by Plato and Aristotle for παιδεία as the long-lasting training for the production of the virtues of character. If ἀκμὴ is the prime of life, and if virtue is the excellence of the character, intellectual maturity as ἀκμὴ is one of the virtues of the epistemic character achieved within the process of education. Discussing the definition provided by Roberts and Wood (2007) about the intellectual firmness as the proper flexibility about “hold”, i.e. our care for the epistemic goods, and the contemporary literature on virtue epistemology, I depict the virtue of intellectual maturity as the disposition to act being oriented by the truth and sensitive to the situations. Grounding on Aristotle’s function argument, I claim that, if virtue is the best way at performing the proper function, intellectual maturity is the way in which an agent performs properly her cognitive tasks. Therefore, intellectual maturity appears to be one of the core elements of the Greek model of rationality. Developing intellectual maturity through the proper training means to lead to the flourishing of the knowledge.