你这个问题有两问，分别回答如下：

第一个问题：题目本身就是个问题，答案是：“不一定”。

1. 在美国英语中，than 可以跟different 连用，相当于from，例如：

German cars are different than ours. 德国造的汽车和我们的不一样。

His way of living is different than ours. 他的生活方式跟我们的不同。

She was different than any other girl he had ever known. 她跟他所认识过的女孩都不同。

He saw he was no different than anybody else. 他认为他与其他人没什么两样。

It won't be much different than today's phone. 现在,它将不会是多不同的比较今天的电话。

You are no different than the rest of them. 你跟其他人没什么不同。

2. than 用于 anywhere,else,other,rather,otherwise 等之后，意为“除…外；而不是”，例如：

She has no other friend than Jane.

除简外她没有朋友。

It was none other than the professor.

不是别人，正是教授本人。

The student is otherwise than his teacher thought.

那个学生并不是老师想像的那种人。

You won't find such freedom anywhere than in our country.

这种自由除我们国家以外其他地方找不到。

He is Tom rather than John. 他是汤姆，而不是约翰。

3. than 用于 barely,hardly,scarcely 之后,表示时间。意为“一…就…”，例如：

Scarcely had I seen him than he spoke to me.

我刚看见他，他就跟我说起话来。

They barely arrived than it was time to leave.

他们刚到就该离开了。

第二个问题：形容词、副词跟than 连用时，一定要用比较级形式的。young 后面有了表示“比较”的than，那么须用younger。