YOU SAID:

i didn't know she was only seven years old i swear

INTO JAPANESE

私は彼女が私が誓う7歳であることを知らなかった

BACK INTO ENGLISH

I didn't know she was seven years old I swear

INTO JAPANESE

私は彼女が7歳だとは知らなかった

BACK INTO ENGLISH

I didn't know she was seven years old.

INTO JAPANESE

私は彼女が7歳だとは知りませんでした。

BACK INTO ENGLISH

I didn't know she was seven years old.