The three stages of river are-
1) Young River - the upper course- This is the beginning of the river. It flows quickly with a lot of energy is called a young river.This fast flowing water creates waterfall and carves out layers of soft rock.
2) Middle aged river- the middle course- This is the middle of a river's journey.Here it gets wider and slows down and called the middle age of the river. Rivers meander (follow a winding path) along the middle course.
3) Old River - the lower course- When the river at last reaches its end of the journey it is called the old river.The end of the river is called mouth.