I see some of you guys don't like the game because of AI cheating, but I think it's actually what makes it much much better game. Just like some others said, because of this you need to fight like a lion during all epochs, and not only that, but even in the later phases of the game.

How does it cheat - by simply having infinite amount of resources, BUT it doesn't use it more than you should be able to handle. Just enough for it to be challenging.

As for me, I haven't played it in a year, but yes, I do have the problem in trying to expand during those non-final ages in the game. However, what is essential for success in this game is patience. You are rarely able to take huge portions of territory at a time. That's why I look where I am able to get some more land with some more resources. Just get there, make a stand, fortify it, start exploiting these resources, and only then continue pushing. This is how I am able to win some land even during Bronze Age, or Middle Age while playing from Prehistoric Age to Industrial Age.

In Rise of Nations AI doesn't cheat like this, but once I take down one opponent I get much more resources and territories. So much that nobody can stand on my after that. Similar to Stronghold Crusader. Once I kill those lords around me, I become so much powerful that they can't stop me. Here the AI keeps biting till the bitter end. Try to look at it as if they had some allies from outside the map. Like the USA to the United Kingdom during WWII. ;)

And yes, the reason for that is the AI is simply not smart enough. But how could you expect from a company to develop an AI as smart as human player? There is no way they could do it. At least not for now, that thing is still ahead of our time.