Pushy old boy, you say, strive to reform (9)
I believe the answer is:
obtrusive
'pushy' is the definition.
(thesaurus)
'old boy you say strive to reform' is the wordplay.
'old boy' becomes 'OB' (abbreviation for a private school 'old boy').
'you say' becomes 'u' ('you' as it sounds).
'to reform' indicates an anagram (letters in a new form).
'u'+'strive'='ustrive'
'ustrive' anagrammed gives 'trusive'.
'ob'+'trusive'='OBTRUSIVE'
(Other definitions for obtrusive that I've seen before include "Unduly prominent" , "Unpleasantly noticeable or prominent" , "Noticeably prominent" , "Unwelcomely prominent" , "Pushing - forward" .)