From, A History of Greek Philosophy, vol. IV, Plato: the man and his dialogues, earlier period,
Cambridge University Press, 19896, pp. 8-38.
The statement that Plato did not hear Socrates speak until he was twenty is attributed by Diogenes himself (3.6) to mere hearsay and introduced as part of the improbable drama of the burning of the tragedy. It is most unlikely that the young kinsman οf Critias and Charmides had to wait so long for the privilege. Another early philosophical acquaintance is said to have been Cratylus the Heraclitean. Aristotle (Metaphysics 987a32) says that Plato was acquainted with him ‘from his youth’, Diogenes (without mention of source) that he ‘attached himself’ to him after the death οf Socrates. There is probably some confusion here, especially as Diogenes (3.5) says that before he heard Socrates, Plato was a Heraclitean in philosophy. Aristotle is more likely to be right, but the chronological sequence is unimportant for the point which he is making, namely that Plato’s two-world metaphysics was the product of an abiding faith, inherited from Socrates, that permanent and stable realities exist combined with a Heraclitean conviction that the whole sensible world was an endless flux of change and instability. Even after Socrates’s death, Plato was only twenty-eight, and had another fifty years of life and philosophy ahead of him.
A Day in Old Athens * A Short History of Greek Philosophy
The Greek Word Library
Reference address : https://www.ellopos.net/elpenor/greek-texts/ancient-Greece/guthrie-plato.asp?pg=6