YOU SAID:

Tomorrow will be my birthday and so I will be another year older.

INTO JAPANESE

明日は私の誕生日なので、また一つ歳をとります。

BACK INTO ENGLISH

It's my birthday tomorrow, so I'm one year older.

INTO JAPANESE

明日は私の誕生日なので、一つ歳をとった。

BACK INTO ENGLISH

It's my birthday tomorrow, so I'm one year older.