你爸爸年纪大了，你得照顾他用英语怎么说？

两个句子要用连接词，不要两个分句独立于一个句子中。
You should take good care of / look after your father, for he is old now.
也可以用because从句，和so从句。
Because your father is old now, you ought to look after him.

Your father is old now , you should take care of him.

your father is old,you should take good care of him.

Your dad is old now ,you ought to take care of him.

Your father is so old that you should take care of/look after him.
我感觉这个相对起来比较合适.呵呵!

Your father is old now,so you should look after him.