Why does the Torah add the words "Asher Chai"?
Rashi and Ramban: Refer to 23:1:3:1.
Or ha'Chayim: He did not live the full amount allotted for him. He died five years earlier, lest he see Esav go off the path (Rashi, verse 30).
Malbim: A person's life is only Avodas Hashem. Without this, he is like an animal! Even though Avraham did not recognize Hashem from birth, he repented and fixed those years, so we can say that he lived all his years. It says so also about Adam ha'Rishon; when he repented, he fixed all his days.
Ha'Emek Davar: A person's life is his Shlemius. Even though Avraham did not recognize Hashem until the age of three or 48, he had the potential from when he was born.
Why does the Torah write "Shanah" (or Shanim) three times?
Rashi: We can expound like for Sarah, 1 - when Avraham was 100, he was like when he was seventy, and at seventy, he was as free of sin as when he was five.
Why does it say "Yemei" regarding the Avos, but not regarding Sarah?