One of the definitions of Leadership states that it is a process of social influence which maximizes the efforts of others, towards the achievement of a common goal.
There is no rule-book in which there is written that one needs to be at some specific age, position to lead others as it has got nothing to do with seniority. One needs to be smart, creative, compassionate to be a good leader no matter what their position or title is. Anyone, who possess these qualities, can become a leader. For instance, in any sports team Captaincy is given to the player who performs well not to the player with the most experience or senior player. In this, leadership skills also play important part in deciding a leader.
All this discussion comes to a conclusion that Leadership is not defined by seniority only.