Gurgeh seems to be in his mid-60's. Special Circumstances seem to have been keeping the Azadian Empire secret since they (allegedly) learned of the Azadian Empire some 74(ish) years ago.

When Gurgeh realises that he was played as a patsy by Special Circumstance, he then heads off on a paranoid tangent, asking whether he was ***bred by SC for the specific purpose of becoming the top Azad player of all time***, thus enabling SC to defeat the Empire from the inside-out.

> 'And when did you first get that sniff of contact?' Gurgeh said, turning to the drone. 'How long have you been sitting on this?'  
The drone hesitated. 'Not long,' it said eventually. 'Seventy-three years.'  
'You people certainly don't rush into things, do you?'  
'Only when we've no choice,' the drone agreed.

and

> 'All my life,' Gurgeh said quietly, looking past the drone to the
> dull, dead landscape outside the tall windows. 'Sixty years… and how
> long has the Culture known about the Empire?'  
> 'About - ah! You're thinking we shaped you somehow. Not so. If we did
> that sort of thing we wouldn't need outsider "mercenaries" like
> Shohobohaum Za to do the really dirty work.'

and

> 'I have learned to recognise the signs,' the professor said. **She was
> twice Gurgeh's age, well into her second century,** but still tall and
> handsome and striking. Her skin was pale and her hair was white, as it
> always had been, and cropped. 'Another of my students humiliated?'