YOU SAID:
彼は来年で51歳になる
INTO JAPANESE
彼は来年で51歳になる
BACK INTO ENGLISH
He will be 51 next year
INTO JAPANESE
いずれそうなる
BACK INTO ENGLISH
He will be.
INTO JAPANESE
いずれそうなる
BACK INTO ENGLISH
He will be.
That didn't even make that much sense in English.