The Torah says:
וַיִּהְיוּ֙ חַיֵּ֣י שָׂרָ֔ה מֵאָ֥ה שָׁנָ֛ה וְעֶשְׂרִ֥ים שָׁנָ֖ה וְשֶׁ֣בַע שָׁנִ֑ים שְׁנֵ֖י חַיֵּ֥י שָׂרָֽה׃ Sarah’s lifetime came to one hundred years and twenty years and seven years -- that was the span of her life. [Genesis 23:1]
Why not just say “one-hundred-twenty-seven years”? The Midrash explains:
When she was 20 she was as beautiful as when she was 7; and at 100 she was as sinless as a woman of 20, which is the age below which Heaven does not punish for sin. [Gen. R. 58:1]
But, as Ramban notes, the same language was used when Abraham [Gen. 25:7] and Ishmael [Gen. 25:17] died, and nobody interpreted it that way (except for Rashi on Abraham, with no source).
So why isn't this language interpreted consistently?
Edit: I am not asking why Ishmael gets a pass, but why the same expression is not explained consistently.