YOU SAID:

I have a brother who is 10 years old

INTO JAPANESE

私は10歳の兄弟がいます

BACK INTO ENGLISH

I have a 10 year old brother.

INTO JAPANESE

私は10歳の兄がいます。

BACK INTO ENGLISH

I have a ten-year old brother.

INTO JAPANESE

私には10歳の兄がいます。

BACK INTO ENGLISH

I have a ten-year old brother.