Ex-pupil (6)
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">ex-pupil</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 old boy that I've seen before include "I say, it's a former school chum" , "my dear chap!" , "Male ex-pupil" , "Male former pupil" , "Alumnus (with network)" .)