My introduction or what got me intrested was Farming Simulator 2009 when I was 10.
The game had amazing mod support and I found out that each mod, like a new tractor, had a modDesc.xml file in it that contained values like in-game price, name of the tractor, fuel tank volume, ... .And I found out that changing these values would change these values in game, which made me feel like an absolute hackerman.