Defense of ancient Enoch authorship

The book of Enoch, from internal evidence - both language and references to other works - is clearly of late authorship, composed some time in the 3rd or 2nd century A.D. The Ethiopian canon is clearly more broad than even the Greek Septuagint. However, they do not claim, nor seek to prove such an early authorship. The point of view of the Ethiopian church is that they honor both scripture and tradition. From http://www.ethiopianorthodox.org/english/canonical/books.html -

The word of God is not contained in the Bible alone, it is to be found in tradition as well. The Sacred Scriptures are the written word of God who is the author of the Old and New Testaments containing nothing but perfect truth in faith and morals. But God’s word is not contained only in them, there is an unwritten word of God also, which we call apostolic tradition. We receive the one and other with equal veneration.

They also clearly accept the late authorship of the book of Enoch:

Among these books is the book of Enoch which throws so much light on Jewish thought on various points during the centuries immediately preceding the Christian era.

The other question here, has there been any attempt to defend or support an early date and authorship? Any attempt to do this is of course ignoring the evidence. Despite that, there is actual evidence that the book of Enoch is preserving a very ancient tradition, that may even go back to the date you suggested. From http://bibeltemplet.net/enoch-southpole.html

Now, over this abyss, where the heavenly fire goes up and down like immense pillars, there are seven stars. This is of course not stars here on earth, but stars hovering over the South Pole horizon. A well known formation of seven stars is the Pleiades. Were the stars Enoch saw the Pleiades? Several things seems to confirm this. Firstly, the angels tells him that certain fallen angels were to be bound to those stars, because of their mingling with women on earth.

This story is very similar to myths in Greece and Mesopotamia. In the Greek myth, seven women were put in the starry heaven because of their mingling with the Titans, by which they were made pregnant. This is also a clear parallel to Genesis 6. And in Enoch, which describes this story in detail, we read, in the chapter after chapter 18, that the women who were seduced by the fallen angels, were to be imprisoned together with those angels, among those seven stars. These Greek women were called the Pleiades, and thereby we know that those seven stars in Enoch must be the Pleiades.

Then there is also a myth from Mesopo­tamia, where seven demons were bound as seven stars in the sky. Also here those stars are identified as the Pleiades.

So, there seems to be a very old and ancient tradition, which found its way not only in the book of Enoch but also in the myths of Greece as well as an ancient tradition in the Middle East. One may surmise these were probably not "angels" at all but rather a race of extraterrestrials, as the Bible itself states that the offspring became a race of giants that inhabited the land of Canaan, before the Israelites wiped them out.

Sort of now this has become an odd "footnote" of Biblical research that no one wants to talk about - even in the early centuries the Jewish rabbis suppressed this sort of interpretation for the "sons of God" in Genesis 6.

There are at least two or three ways to possibly give this question a plausible answer, while at the same time safeguarding the Alexandrian Traditions' position on the subject of the Book of Enoch.

The first point to take into account is the fact that the only complete extant copy of the Book of Enoch is written in the Ge'ez language. This particular point does not answer the question, but merely shows why these Churches of North Africa are so attached to this book. The actual original language is unknown. It may have been Hebrew or Aramaic.

The next point to be made is that, as in the case with most of the different rites that were founded by one of the apostles or their disciples, there are many viable customs and traditions have been handed down to us from Time Immemorial. As such, no proof can truly be found, since it seems to possibly be in the domain of the Ethiopian Church's custom to believe that the Book of Enoch was written by Enoch himself. There are many pious customs and beliefs which cannot be verified one way or another. This one is no exception.

The Book of Enoch was not included in the Christian canon of books in the 4th century and is regarded as Scripture in only the Ethiopian Orthodox Church and the Eritrean Orthodox Church. Why? I think that Tertullian (155-240) holds the key!

"Regarding the quotation in Jude, most of early Christianity considered it an independent quotation pre-dating the flood. Regarding the Book of Enoch itself Origen, Jerome and Augustin mention it, but as of no authority. Justin, Athenagoras, Irenaeus, Clemens Alexandrinus, Lactantius, and others borrowed an opinion out of this book of Enoch, that the angels had connection with the daughters of men, of whom they had offspring ('the giants of the past'). Tertullian, in several places, speaks of this book with esteem; and would persuade us, that it was preserved by Noah during the deluge." Taken from this Wikipedia link: Enoch (ancestor of Noah).

And Again:

The Epistle of Barnabas, young Origen, Clement of Alexandria, and Tertullian all considered 1 Enoch to be Scripture. Tertullian wrote in "Concerning The Genuineness Of 'The Prophecy Of Enoch,' I am aware that the Scripture of Enoch, which has assigned this order (of action) to angels, is not received by some, because it is not admitted into the Jewish canon either…But since Enoch in the same Scripture has preached likewise concerning the Lord, nothing at all must be rejected by us which pertains to us; and we read that 'every Scripture suitable for edification is divinely inspired.'…To these considerations is added the fact that Enoch possesses a testimony in the Apostle Jude." [Tertullian, "On the Apparel of Women,"in The Ante-Nicene Fathers: Fathers of the Third Century: Tertullian, Part Fourth; Minucius Felix; Commodian; Origen, Parts First and Second, ed. Alexander Roberts, James Donaldson, and A. Cleveland Coxe, trans. S. Thelwall, vol. 4 (Buffalo, NY: Christian Literature Company, 1885), 15. Is Enoch Scripture?

Hope this helps.