Conversation so far:
how old was Imran khan at the height of his career?
At the height of his career, in 1982, the thirty-year-old Khan took over the captaincy of the Pakistan cricket
how old was Imran khan when he took the last winning wicket?
At the age of 39, Imran Khan took the winning last wicket himself
who was Imran khan?
Imran Khan is the 22nd and current Prime Minister of Pakistan. Imran Khan was also an international cricketer and captain of the Pakistan national cricket team

Question: when was he captain?
Self-contained rewrite: when was Imran Khan captain?