I believe that there would be commentaries of the Torah older than 1 BCE and that can shed significant light on what the message of God is in terms of its authoritativeness. Israelites have a glorious history of the Kingdoms of David, Israel and Solomon, and it is quite impossible to not have commentaries by respectable Rabbis before 1 BCE. Can people here point me to where are they to be found? After all, inasmuch as the Torah of old was preserved, it is fair-seeming that the interpretations of old should also have been preserved.
The difficulty with your question is as follows:
In those days (almost) everything was oral. For example we have lots of things the Hillel said (he lived around then), but they were not written down then - they were written down later. So do they count? They are certainly commentary, but they were only written down later. The Talmud is full of things that were said back then, but they are not collected into a single text with a date from around then. (i.e. the Targumim that Double AA mentioned).
Secondly things written down then became the source material of today. Maybe in those days (well, much earlier actually) things like Proverbs and Psalms were considered commentary, but today they would be considered source material. So again, do they count for your question?
Here is a chart: http://www.myjewishlearning.com/texts/About_Jewish_Texts/Jewish_Texts/Timeline.shtml of complete works with a date. (The formatting is terrible, the last column is only partially visible, and note that it includes some works that are not considered authoritative today, i.e. Apocrypha.)
The rarity of complete works from that early is part of the reason we consider the complete works we do have to be source material and not commentary. (People certainly told stories orally, and some short things were written down, but very little book length material exists from back then - which is why the Torah has such a special place in history.)
The same question, roughly, was asked of Rav Sherira Hagaon (ca 900-1000, Babylonia), one of the last heads of the Pumbedisa Yeshiva, the school of rabbinic scholarship which had existed in Babylon from after the destruction of the First Temple until the 11th Century of the Common Era. In his Iggeres (although the term Iggeres means a "letter" it is much longer) he traces the history of rabbinic knowledge and scholarship from the giving of the Torah, written and oral, to Moses, the transmission to Aaron, Joshua and the Elders, the Judges, Prophets, the Zugim -- the joint leaders of the Academy and Beis Din (courts) in Jerusalem -- and then to the rabbis of the late 2nd Temple generation. In those years, he explains, the written and oral law, including interpretations of the Written Torah, were passed down orally from generation to generation and, because students stayed close to their teachers, the chain of tradition was neither forgotten nor confused. Hillel and Shammai, who were the zuggim from the generation just before the beginning of the common era, were known to personally disagree on only three issues. However, in the subsequent generations, the capability of the rabbis to orally transmit the traditions radically changed with the brutal Roman occupation, especially following the destruction of Jerusalem and the Holy Temple, and the dispersion of the rabbis to Yavneh, Tiberius, and other places. Thereafter, although there was broad agreement on most general points, on specific laws and customs there were often disputes because somewhere there had been an error in transmission. Rav Sheriera explains that these errors were caused because the occupation led to students not being able to fully devote themselves to their teachers, and the inability to check with colleagues to assure that one rabbi taught Torah in the same way.
By the second century of the Common Era, there had come to be some agreement that the oral Torah could not continue to be conveyed exclusively by oral means, but had to be written down. Almost simultaneously Rabbi Yehuda HaNasi ("Rebbe") and Rabbi Chiyah wrote down what they knew of the memorized rabbinic teachings in what became known as the Mishna and the Tosefta, respectively. Individual teachings from the Tosefta are frequently referred to in the Talmud as B'raisas. After the publication of the Mishna, scholars in Israel and Babylonia continued to study Rebbe's and Rabbi Chiyah's versions of the mishnayos attempted to reconcile seemingly conflicting teachings. After several generations of these discussions, the Israeli contingent of teachers preserved their studies in a collection of books now known as the Jerusalem Talmud (ca 4th century), and the Babylonian Talmud (ca late 7th century).
In summary, we have no writings of commentaries before the 1st century of the Commen Era because the rabbis at that time believed that writing down the oral teachings G-d gave to Moses to be forbidden and unnecessary. But during Roman rule, writing down the Oral law became a necessity.