Glacial period (3,3)
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">glacial period</span>' is the definition.<br/ ><span class="explanation-format__explanation">(synonyms)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for ice age that I've seen before include "Freezing era" , "'When glaciers covered the earth (3,3)'" , "Period of extreme cold" , "Cold period for Earth" , "Glacial period" .)
(Another definition for iceage that I've seen is " Period of extreme cold".)