Of tender years (5)
I believe the answer is:
young
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">of tender years</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for young that I've seen before include "Not yet grown" , "no wrinkly!" , "Offspring; immature" , "issue" , "like Lochinvar?" .)