我最近总是感到乏力。

That means you're over the hill.

那是因为你在走下坡路。

Now, he is over the hill.

现在，他在走下坡路。

over the hill

走下坡路

"走下坡路"怎么说?

If I'm too old to cut the mustard, maybe I should retire.

如果年纪大了不能胜任，我可能就会隐退

Cut the mustard

胜任

He can't cut his mustard.

他不能很好地完成分内工作。

If he can't cut the mustard, we'll have to find someone else to do the job.

如果他没能力完成自己的工作，我们会找他人来做。