Very great age of octogenarian, male, not English (6)
I believe the answer is:
mighty
'very' is the definition.
('mighty' can be a synonym of 'very')
I can't explain the rest of the clue.
Can you help me to learn more?
(Other definitions for mighty that I've seen before include "Extremely" , "Powerful and great" , "Powerful - huge" , "Having great strength" , "Strong, powerful" .)