Age group (10)
I believe the answer is:
generation
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">age group</span>' is the definition.<br/ ><span class="explanation-format__explanation">(thesaurus)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for generation that I've seen before include "what was lost in WW1" , "People of the same age" , "group of similar age" , "About thirty years'" , "peer group" .)