YOU SAID:
I will die when I am ninety
INTO JAPANESE
私が90歳の時に私は死ぬだろう
BACK INTO ENGLISH
I will die when I am 90 years old
INTO JAPANESE
私が90歳の時に私は死ぬでしょう
BACK INTO ENGLISH
I will die when I am 90 years old
That didn't even make that much sense in English.