3. Although/Though he is a child, he knows a lot of Chinese characters.

　 →Child(省略冠词)as/though he is, he knows a lot of Chinese characters. 他虽然还是个孩子，却认识了许多汉字。

2. Although/Though I respect him very much, I cannot agree with his idea.

　 →Much as/though I respect him, I cannot agree with his idea. 虽然我很尊重他，但是我不同意他的观点。

1. Although/Though I’m young, I already know what career I want to follow.

→Young as/though I am, I already know what career I want to follow.

我虽然年轻，但我已经明白我应该追随什么样的事业。