简单点的说法：

①He's no longer popular.

高级一点：

②He's no longer in his prime.或He's now past his prime.（已过鼎盛期）

③He had his moments.（曾有过辉煌）

④He's a has-been.（过气人物）

可以表达“过气”的词组：

1 a has-been 指过气的人物。

If you describe someone as a has-been, you are indicating in an unkind way that they were important or respected in the past, but they are not now.

例句：

He became famous overnight / at that time, but now he is just a has-been.

他那时候一夜成名，但现在已经过气了。

2 over the hill 指风光不再，开始走下坡路。

从字面意思看，这个短语就是翻过山坡的意思，翻过山坡不就是要走下坡路了嘛。用来形容人的时候，就是指已经过了鼎盛时期了，开始慢慢往下走了。

例句：

I don't think of myself as being over the hill yet.

我不认为我已经在走下坡路了。

3 a spent force 指过气、昨日黄花。

释义：Someone who no longer has the power or influence he once had.

例句：

The new album is proof that this band is not a spent force just yet.

新专辑证明这支乐队还远没有过气。

4 over party 指某人或某风潮过气了，在俚语中可理解为人走茶凉。

释义：When a trend or a person is over.

例句：

He's over party.

他过气了。

She should go to her own over party.

她过气了。