Firstborn among siblings
I believe the answer is:
eldest
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">firstborn among siblings</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for eldest that I've seen before include "The oldest of three or more" , "Most senior of two" , "Most advanced in years" , "heir?" , "Most advanced in age, led set (anag.)" .)