Maturer when going wrong, making mistake (7)
I believe the answer is:
erratum
'mistake' is the definition.
(erratum is a kind of mistake)
'maturer when going wrong' is the wordplay.
'when going wrong' indicates an anagram.
'maturer' with letters rearranged gives 'ERRATUM'.
'making' acts as a link.
(Other definitions for erratum that I've seen before include "Printing error" , "Published correction" , "mistake in text" , "Printer's mistake" , "Faux pas" .)