Isambard, the dating of the book of Daniel is discussed in depth online. Try Wikipedia for an overview. Don't look for so called 'Bible scholars' as they have an agenda to fulfill. Look for academics at professor level who know the texts, the relevant secular history and the archaeology.
Superficially it is an easy thing to prove because the writer of Daniel cannot predict the events immediately ahead of 162 BCE but gets the previous years correctly applied as if he prophesied them. Also a major blow to traditional dating is that nobody anywhere quotes Daniel until the middle of the second century BCE. This is a significant exception relating to to the criteria for what made a writing a Biblical text.
There are strong counter-arguments to a late dating as is the nature of the dating of any manuscripts including the first uses of the style of language and word use of the specific texts. However it must always be remembered that nothing is sacred in handwritten documents, there always has to be considered the allowance for forgeries, insertions, deletions and deliberate archaising within a hand-copied text.
Going back to your point of "Daniel's" image, it is a borrowing from a much older piece of writing from the 7th century BCE by the Greek poet Hesiod in his work Theogony. In it he portrayed man's history through an allegory of an image of different metals successively decreasing in worth from a fabled golden race down to powerful empires represented by iron.
It remains a good example of how much of the Bible is a crib from earlier sources, in this case pre-classical Greek. This method shows the poverty of inspiration in the Bible where most of it is copied from paganism and re-worked to suit the propaganda interests of the commissioners of the work.
Once departing from the JW religion it is best to realize early on, that contrary to the force and habit of cult belief, nothing in the Bible has meaningful significance for us today.
