The ambiguity in dates is a classic ‘stream and sequence’ effect analogous to the same in the ‘myth’ of Moses. The Exile in the Israelite tradition shows the way Israelitism and Zoroastrianism blended together in the emergence of monotheism…Cf. World History and the Eonic Effect
There is no consensus on the dating of Zoroaster; the Avesta gives no direct information about it, while historical sources are conflicting. Some scholars base their date reconstruction on the Proto-Indo-Iranian language and Proto-Indo-Iranian religion, and thus his origin is considered to have been somewhere in northeastern Iran and sometime between 1500 and 500 BC.Some scholars such as Mary Boyce (who dated Zoroaster to somewhere between 1700 and 1000 BC) used linguistic and socio-cultural evidence to place Zoroaster between 1500 and 1000 BC (or 1200 and 900 BC). The basis of this theory is primarily proposed on linguistic similarities between the Old Avestan language of the Zoroastrian Gathas and the Sanskrit of the Rigveda (c. 1700–1100 BC), a collection of early Vedic hymns. Both texts are considered to have a common archaic Indo-Iranian origin. The Gathas portray an ancient Stone-Bronze Age bipartite society of warrior-herdsmen and priests (compared to Bronze tripartite society; some conjecture that it depicts the Yaz culture), and that it is thus implausible that the Gathas and Rigveda could have been composed more than a few centuries apart. These scholars suggest that Zoroaster lived in an isolated tribe or composed the Gathas before the 1200–1000 BC migration by the Iranians from the steppe to the Iranian Plateau. The shortfall of the argument is the vague comparison, and the archaic language of Gathas does not necessarily indicate time difference.Other scholars propose a period between 7th and 6th century BC, for example, c. 650–600 BC or 559–522 BC. The latest possible date is the mid 6th century BC, at the time of Achaemenid Empire’s Darius I, or his predecessor Cyrus the Great. This date gains credence mainly from attempts to connect figures in Zoroastrian texts to historical personages; thus some have postulated that the mythical Vishtaspa who appears in an account of Zoroaster’s life was Darius I’s father, also named Vishtaspa (or Hystaspes in Greek). However, if this were true, it seems unlikely that the Avesta would not mention that Vishtaspa’s son became the ruler of the Persian Empire, or that this key fact about Darius’s father would not be mentioned in the Behistun Inscription. It is also possible that Darius I’s father was named in honor of the Zoroastrian patron, indicating possible Zoroastrian faith by Arsames.
Source: Zoroaster – Wikipedia