Same sort of thing happened to me back in 2003, there was this cocky guy who'd challenged everyone who went to this internet cafe and usually beat them all, he would do what you do, let them win a bit, and crush them later. I decided to take some time learning how he builds up, his timings, placement and what not, he'd almost always position his paladins at a certain area of the map, i don't remember the name of the map, there was a lake in the middle and the only connection is either from the north east or southwest.
I decided to go ahead and play against this guy and a bet that whoever losses gets to buy the winner eggrolls, he had seen me play before against some AI, and i was pretty bad then. The game started and he did his old routine, small attacks with which he would try to pick off my workers, he did well on that, i teched up faster but i was losing, bad, i sort of gave up and decided to call it quits, when this guy decides to build a monument/wonder?, realizing that he would have spent a ton of resources on that and would have an inferior army, i decided to counter attack from the north, with a decent defensive line of heavy catapults, a tower and some cavalry.
I kept the pressure on from the north, seeing this, he starts building a wall near the wonder and a few towers, and i started to rally my troops a safe distance from his defensive line. And he started doing his thing, bunch of paladins running down towards the south, but this time, it is a lot smaller than what he would have in other games. They put up a decent fight but i came out victorious, i push up my remaining cavalry from the south, and started setting up my seige weapons near the wall. This is where he starts to build a bunch of ships on the lake, transports, fuckton of transports, he loaded all his remaining units on the ships and went to the middle of the lake.
I went on to destroy his base, and now he's fully visible on the map, with my cavalry running around the map to stop his little attacks on my land. This went on for about 10 minutes until i build some galley to just kill of his remaining troops.
He just laughed off my win and didn't pay the eggrolls.
tl;dr. boring story about how i won a game of aoe.