The Rockies are actually relatively recent, 55M to 80M years old. The Appalachians are much older and part of the reason they aren't anywhere near as big as (for example) the Rockies, is because they have been eroded for so much longer. That said, they are still definitely not the oldest mountain range. It looks like the Makhonjwa Mountains win that one.
I agree, this kind of thing is awesome. Like in the original meaning of the term too... inspiring of awe.