YOU SAID:

I play the trombone since 6 years

INTO JAPANESE

私は6年からトロンボーンを演奏しています

BACK INTO ENGLISH

I have been playing trombone since 6

INTO JAPANESE

私は6歳からトロンボーンを演奏しています

BACK INTO ENGLISH

I have been playing trombone since 6 years old

INTO JAPANESE

私は6歳からトロンボーンを演奏しています

BACK INTO ENGLISH

I have been playing trombone since 6 years old