Since when do human beings start to know how to calculate ? Its hard to give a precise answer. However, its been way since 2000 years B.C. when there were calculations with certain degree of complexity. The oldest source of mathematics found so far is a sketch on papyrus from the great egypt kingdom around 1650 years B.C. On the sketch, there was an interesting question:
[There are 7 rooms, each room has 7 cat, each cat caught 7 mouse, each mouse ate 7 straws of wheats, each straws has 7 wheats. How much wheat has been eaten?]
During that timeframe, this question is considered to be a tough question.
cat: 7 x 7 = 49
mouse: 49 x 7 = 343
Straws: 343 x 7 = 2401
Wheat: 2401 x 7 = 19600