The year of Diogenes’ birth cannot fixed with certainty. Diogenes Laertius informs us that he was already an aged man in the 113th Olympiad (324 – 321 B.C), and elsewhere notes that he was nearly ninety years old at the time of his death. The year of his death appears to be reasonably well established as one of the few facts known with some certainty about Diogenes. According to Demetrius of Magnesia and Suidas, his death occurred on the same year of Alexander ‘s death in Babylon (423 B.C), and plutarch calls attention to the even greater coincidence that Diogenes and Alexander died on the very same day, witch is also reported by Diogenes Laertius. Still, the constant juxtaposition that we encounter in the sources between the defiant Cynic philosopher, a contemptuous man who looked with disdain upon Alexander and upon enormous political edifice for witch he stood, on the one hand , and, on the other, the proud and vain Macedonian emperor, who embodied much of what Diogenes viewed as the source of human ills --- this juxtaposition may have justified the necessity of biographers to have them die precisely at the same time. Nevertheless in the absence of contradictory evidence, it may be reasonable to assign the year 323 B.C as the year of Diogenes death.
The year of his birth presents certain problems that cannot be satisfactorily solved. If as Diogenes Laertius maintains, he was ninety or nearly ninety at the time of his death, he would have been born around the year 413 B.C. There are, however, reports that speak of him as having been eighty one years old when he died, as in the testimony of Censorius, and we read in Suidas that his birth occurred during the reign of the Thirty in Athens, witch lasted ten months in the year 404 B.C. The Thirty were a group of Athenians oligarchs who, under the leadership of Critias and with the blessing of the victorious Spartans, assumed power at the end of the Peloponnesian War. We hear reports, however of Diogenes having been involved in the defacement of coinage in Sinope as early as the fourth decade of the fourth century, and we learn from the Chronicon Paschale the he was a well known man before the year 462 B.C, although neither the reason for his fame nor the place where he was famous is mentioned. If this report is historically correct, there should be no reason for not pushing back the time of his birth to the year suggested by Diogenes Laertius, that is 413 B.C, for then Diogenes would have been a middle age man when the famous defacement of the coinage might have taken place. An early date for Diogenes’ birth moreover, allows us to consider as more plausible some biographical relationship between Antisthenes and Diogenes. Antisthenes birth may be placed as early as in the year 455 B.C. These parameters make possible a reasonable period of association between these two philosophers an association that is of some significance with respect to the issue of the origins of Cynicism. There  is also the possibility entertained by some scholars that even before his alleged banishment from Sinope, Diogenes could have visited Athens where surely he would have come across Antisthenes and others among Socrates’ associates.