1. he is 2 years younger than me
2. he speaks English as well as me
3太阳是所有星星中最大的 - 这句话错了
但勉强字面上帮你翻译
the sun is the biggest of all stars
4他回家作业与他姐姐做得一样仔细 - LZ打错了吧
5. I don't run as fast as him
6. i'll try my best to speak in English as often as I can
7. he eats as little as possible in order to stay slim
8. the thief ran away as quickly as possible