over the hill ----------- 走下坡路（成语）

英文释义
(IDIOM) Describing someone who is too old to be as useful as in previous times.

例句
For many years my brilliant uncle was the best executive in his company, but now I think he's over the hill because his business decisions are not very good, and he often falls asleep at meetings.
多年来，我的聪明的叔叔一直是公司里最优秀的高管，但现在我觉得，他在走下坡路，因为他的商业决策不是很好，开会时也总是睡着。