Time, it is true that there is much conjecture in this area. But the Celts are given in the literature as Iron Age, not Bronze Age. Now I know that this "Age" thing is a variable depending where in the world you are. My beliefs are not purely taken from oral traditions but a mix of written and oral. Depending 100% on either is a mistake. So you come to a situation where no-one is 100% wrong or right. We must avoid dogmatism and utter reliance on the written word which is often just a reiteration of previous writers opinions. Personally, I rely on writers from British Universities.
Best example I can think of is the Bible. OT is the tribal records of a small number of people in the Middle-East. NT written centuries after the "events". The whole bang-shoot translated several times, revised several times, subject to deletions and political censoring. Care to put a number of how true the whole thing is ?
Early European histories written by christian monks - biased or not ?