Renou p. 483. Louis Renou, "Pāṇini" in Thomas Albert Sebeok et al., ed., Current Trends in Linguistics vol. 5 (Hagae: Mouton, 1969) pp. 481-498, praecipue p. 483 (Paginae selectae apud Google Books)
"The date ... is usually assumed to be about 350 B.C., but . . . it is perhaps safer to say that he lived after, and perhaps soon after, 500 B.C.": A. A. MacDonell, India's Past: A Survey of Her Literatures, Religions, Languages and Antiquities (Oxonii: Oxford University Press, 1927) pp. 136-137 (Paginae selectae apud Google Books)
"Generally, I have decided, without absolute certainty, on the 4th or 5th centuries B.C.": Renou p. 483 Louis Renou, "Pāṇini" in Thomas Albert Sebeok et al., ed., Current Trends in Linguistics vol. 5 (Hagae: Mouton, 1969) pp. 481-498, praecipue p. 483 (Paginae selectae apud Google Books)