YOU SAID:

I once was a young boy

INTO JAPANESE

私はかつて少年だった

BACK INTO ENGLISH

i was once a boy

INTO JAPANESE

私はかつて男の子だった

BACK INTO ENGLISH

i used to be a boy

INTO JAPANESE

私は男の子だった

BACK INTO ENGLISH

i was a boy

INTO JAPANESE

私は男の子でした

BACK INTO ENGLISH

i was a boy