He was once in Big House — age, about 90 (2,3)

I believe the answer is:

ex con

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But I can't explain it at all! Could you help me understand?

(Other definitions for ex con that I've seen before include "One now unrestrained" , "whose time is over?" , "He was in prison" , "political defector?" , "One now liberated" .)

I've seen this clue in The Hindu.

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