YOU SAID:

under a tree where the grass don't grow we made a promise to never get old

INTO JAPANESE

草が育たない木の下で、私たちは決して年を取らないと約束した

BACK INTO ENGLISH

Under a tree that doesn't grow grass, we promised never to grow old

INTO JAPANESE

草が生えない木の下で、決して年をとらないと約束しました

BACK INTO ENGLISH

I promised I would never grow old under a tree that doesn't grow grass

INTO JAPANESE

私は草を育てない木の下で年を取ることは決してないと約束した

BACK INTO ENGLISH

I promised I would never grow old under a tree that doesn't grow grass