The Prime Minister of India, at the time of his/her appointment
The Prime Minister is appointed by the President. The minimum age required is 25 years, as he can be the member of either house if not, must be within 6 months. In normal circumstances, the President can hardly exercise his discretion; the President's choice to appoint the Prime Minister is restricted to the leader of the Party with majority of Lok Sabha.
The correct option is B.