Cousin, I am too young to be your father, Though you are old enough to be my heir. (3.3.8)
Richard expresses his real issue with Henry Bolingbroke: they share a bloodline. Still, Bolingbroke is breaking with tradition by seizing the crown: instead of the eldest son passing on the throne to his eldest son, Bolingbroke, a cousin, is stepping in. Richard invokes the old model of inheritance in order to show how Bolingbroke is breaking it. He tells Bolingbroke that he is too young to be his father – in other words, that Bolingbroke is messing with the system. By taking power, he is writing himself into history, not as Richard's son but as his heir. Because of his intervention, "son" and "heir" aren't synonyms anymore.