What defines an Age?

[Arvedui]

In another attempt at bringing some life into these dark and murky halls, I bring here a couple of questions that have bothered me lately:

1) What denotes the ending of an Age?
The First Age ended when Morgoth was overthrown and cast into the Void.
The Second Age ended when Sauron was overthrown in the Battle of the Last Alliance?
The Third Age ended when Sauron was overthrown for the second time (some people never learn...).
So does an Age (of the Sun) come to an end when some major evil have been overwon?

2) Tolkien stated somewhere (can't remember exactly where) that the world was in the beginning of the Sixth Age. Does anyone have any ideas or rather suggestions as to what denoted the end of the Fourth and Fifth Ages?

[Gothmog]

So does an Age (of the Sun) come to an end when some major evil have been overwon?

While this seems to have been the case for the first three ages of the Sun. It was not so for the Ages of the Trees. Three Ages of which Melkor spent in quiet contemplation in the Halls of Mandos. So I doubt that it would be necessesary that a Great Evil be defeated but rather that some truly notable event happens.

The End of the Fourth Age? Now then this age began with the overthrow of Sauron and the return of the Line of Kings to Gondor and Arnor reuniting the two kingdoms once more. Perhaps the End of the Fourth Age came about when that line finally ended as a ruling house and United Kingdom of Gondor and Arnor became once more devided into smaller kingdoms and princapalities.

[Lhunithiliel]

While analysing facts about the First Age of the Sun - Lecture 1 (http://www.thetolkienwiki.org/wiki.cgi?action=browse&id=FirstAge&oldid=The__First__Age__of__the__Sun) , I in fact realised that each Age ends with a major military conflict that usually leads to a drastic change in the course of the history of ME. Then comes a period of peace, which unfortunately does not last too long and so the arising new conflicts lead again to a last major one and thus another Age is ended...

I think the Fourth Age will have the same "destiny", having in mind the "New Shadow".
Just a thought... :rolleyes:

[Inderjit S]

Each age last's about three thousand years. The first, second and third all lasted around about that time, give or take.

We are now in the Seventh Age, according to Tolkien.

[Finduilas]

2) Tolkien stated somewhere (can't remember exactly where) that the world was in the beginning of the Sixth Age. Does anyone have any ideas or rather suggestions as to what denoted the end of the Fourth and Fifth Ages?

Which world?Ours or ME?
About ME:

Tracing the History of ME, we see that every Epoch starts with a 'creation' and finishes with a 'destruction'.

'Pre'- Age :
The creation of Arda.The rebellion of the Noldor.
I Age :
The Awaking of Men. The destruction of Beleriand.
II Age :
The 'creation' of Numenore. The First Fall Of Sauron (and Numenore).
III Age :
The 'creation' of the Shire. The Second Fall of Sauron (and the leaving of the Elves).
IV Age :
The 'creation' of the United Kingdom. -?-

So considering a little bit more carefully we see that the 'creation' causes the 'destruction'. The Noldor are not pleased with their rights (not being immortal) and therefore, they revolt.
Men cause the destruction of Beleriand.
The Fall of Sauron is inevitably connected with the Numenorean Kings.
The Second Fall of Sauron is most inevitably connected with the Shire.

So it is logical to think over what could the Union do to ME, so catastrophic that the end would be a destruction.
I will develop an idea, having in mind our Real World attitude of thinking concerning Wars and Unions.

We have the Downfall of Sauron. All ME peoples are free. But here comes the major problem. Until now, everybody has lived separately, and it was the War that united them, made them close. The people from the lower stratum (villagers, farm workers etc.) have got used to being helped, being treated well and woth good intentions. But the war is over. The Union is built and life continues.
As we know, people of Gondor are proud people, it is in their venes to rule, to command. And as it happens, history repeats itself. The people of Gondor turn into the Second people of Numenore. In the beginning proud and noble (probably during the kingship of Aragorn and his descendants) but soon become greedy for more and more power, lands to rule.
And so the Union decides to appropriate some lands for itself. Thus the Union turns into an Empire. But an Empire is not to last long.
And thus the IV Age finishes with the revolt of the people of ME against the Gondor Empire.
It might not happen so and many might disagree but it's just a possibility.