YOU SAID:

Approaching the speed of light, a person inside a spaceship would age much slower than his twin at home.

INTO JAPANESE

光の速度に近づく、宇宙船の中の人の自宅に彼の双子よりも遅く年齢。

BACK INTO ENGLISH

Approaching the speed of light, in the spaceship's home more slowly than his twin age.

INTO JAPANESE

彼の双子の年齢よりもゆっくりと宇宙船の家で、光速に近づいています。

BACK INTO ENGLISH

His twin older than are approaching light spaceship home, slowly.