Best time of youth (5,4)
I believe the answer is:
salad days
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">best time of youth</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 salad days that I've seen before include "inexperienced youth" , "Green term" , "Period of youth and inexperience - ate lettuce dishes?" , "Time of youth and inexperience" , "Period of youthful inexperience" .)