Ozone damaged, I see, by this age (7)
I believe the answer is:
neozoic
'this age' is the definition.
(I have seen 'old age' mean 'neozoic' so perhaps 'age' could also mean 'neozoic')
'ozone damaged i see' is the wordplay.
'damaged' is an anagram indicator.
'see' becomes 'C' (the word for the letter, according to Chambers).
'ozone' with letters rearranged gives 'neozo'.
'neozo'+'i'+'c'='NEOZOIC'
'by' is the link.
(Other definitions for neozoic that I've seen before include "recent years" , "of a certain age" , "old age" , "recent geological period" .)