He's a nice old fellow.

这位老兄人不错。

I saw a young fellow.

我看到一个小伙子。

We are school fellows.

我们是校友。

She has a very good reputation among her fellows.

她在同事中口碑甚佳。

He recalled his fellow traveller with pleasure.

他愉快地回忆起他的旅伴。

fellow workers / students / travellers

同事/同学/旅伴