YOU SAID:

i overheard that she was 19

INTO JAPANESE

彼女が19歳だったのを聞いた

BACK INTO ENGLISH

I heard she was 19 years old

INTO JAPANESE

彼女は19歳だったそうです

BACK INTO ENGLISH

She was 19 years old

INTO JAPANESE

彼女は19歳でした

BACK INTO ENGLISH

She was 19 years old