很早以前我就知道这个公司了(请翻译成英文,谢谢)

hear about是“听说”的意思，为终止性动词，后面不能接表示一段时间的短语作状语。
可以说，I heard about the company long ago.
或者：I have known (about) the company for long.

I've heard about this company long ago.

I have knew this company for a long time.

i've heard about this company for long.

I've known(heard about) this company so long ago

很早以前是long long ago
I knew the company long long ago.
或：I have known the company for a long time.