Old boy (7)
I believe the answer is:
alumnus
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">old boy</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for alumnus that I've seen before include "US college old boy" , "Past pupil" , "Former school pupil" , "Old pupil" , "(US) college graduate" .)