I meant that very little of Aztec history is recorded in a way that survives today.

My understanding - which may be wrong - is that it's at the level of much older high civilization. And I think that makes them "feel" as old as those civilizations, because we know so little.

I'm not sure the Aztecs were that technologically behind. The main reason they and all the other New World peoples lost was their less robust immune system. Typically, 80-90% of the population died of European diseases as soon as - or often even before - the Europeans arrived.

This was 300 years before germ theory, so no one on either side knew what was happening.