Fully developed (6)
I believe the answer is:
mature
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">fully developed</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 mature that I've seen before include "Age" , "Grown-up" , "Full-grown - ripe" , "due to be paid" , "Grow older" .)