YOU SAID:

Someone took the fancy necklace that my mother gave me when I turned 18

INTO JAPANESE

私が18歳になったときに母がくれた豪華なネックレスを誰かが取りました

BACK INTO ENGLISH

Someone took the gorgeous necklace my mother gave me when I was 18

INTO JAPANESE

私が18歳のときに母がくれた豪華なネックレスを誰かが取った

BACK INTO ENGLISH

Someone took the gorgeous necklace my mother gave me when I was 18