Days and years on earth rising? Blimey! (4)
I believe the answer is:
egad
'blimey' is the definition.
(both are expressions of surprise)
'days and years on earth rising?' is the wordplay.
'days' becomes 'd' (abbreviation for days).
'and' is a charade indicator (letters next to each other).
'years on earth' becomes 'age' (I am not sure about this - if you are sure you should believe this answer much more).
'rising?' says the letters should be written backwards (going up in a down clue).
'age' in reverse letter order is 'ega'.
'd' put after 'ega' is 'EGAD'.
Can you help me to learn more?
(Other definitions for egad that I've seen before include "Christ" , "Old exclamation; aged (anagram)" , "Mild oath - aged (anag)" , "My word once" , "Forgotten curse" .)