YOU SAID:

he's gonna think you're serious. his brain isn't fully developed to understand that.

INTO JAPANESE

彼はあなたが本気だと思うだろう。彼の脳はそれを理解するために完全には発達していません。

BACK INTO ENGLISH

He will think you are serious. His brain is not fully developed to understand it.

INTO JAPANESE

彼はあなたが本気だと思うでしょう。彼の脳はそれを理解するために完全には発達していません。

BACK INTO ENGLISH

He will think you are serious. His brain is not fully developed to understand it.