Trivia and Riddles

Peirush Da’as Zekenim writes that even though the verse says that Sarah Immeinu lived for 127 years, she began her true life at the age of 90, when she gave birth to her son Yitzchok. Da’as Zekenim says that the hint to it is in the first 3 words of the parsha (”ויהיו חיי שרה”). Can you figure out how that is hinted in those words?