My thoughts of this are that he kept the Triforce of Courage until the Link in ALBW was worthy of having it and that's why he lived way beyond a normal lifetime. And if this is true, then maybe the Zelda from ALttP did the same with the Triforce of Wisdom & gave it to the Zelda from ALBW & became the Impa of ALBW after living beyond a normal lifetime thanks to the Triforce of Wisdom.