YOU SAID:

this person has been my childhood friend since we were in first grade.

INTO JAPANESE

私たちが1年生の時から、この人は私の幼なじみでした。

BACK INTO ENGLISH

This guy has been my childhood since we were a freshman.

INTO JAPANESE

私たちが新入生だったので、この男は私の子供時代でした。

BACK INTO ENGLISH

This guy was my childhood because we were freshmen.

INTO JAPANESE

私たちは新入生だったので、この男は私の子供時代でした。

BACK INTO ENGLISH

This guy was my childhood because we were freshmen.