YOU SAID:

He can't leave his room until 10 o'clock.

INTO JAPANESE

彼は10時まで部屋から出ることができません。

BACK INTO ENGLISH

He cannot leave his room until 10 o'clock.

INTO JAPANESE

彼は10時まで部屋から出ることができません。

BACK INTO ENGLISH

He cannot leave his room until 10 o'clock.