In the Name of God, the Compassionate, the Merciful.
Hi!
Conversation
A: It’s an ugly day today.
B: I know. I think it may rain.
.
.
B: I really wish it wasn’t so hot every day.
A: Me too. I can’t wait until winter.
B: I like winter too, but sometimes it gets too cold.
.
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Is “I can’t wait until winter” an idiom?
Thank you
In this context, “I can’t wait” means highly anticipating. Any wait seems long. It is usually said enthusiastically, so when written it might call for an exclamation mark.
The person is saying that they don’t like the hot weather. So they are highly anticipating winter when it will be cooler.
I’m really hungry. I can’t wait for dinner.
I’m tired of school. I can’t wait to graduate.
This is a long drive. I can’t wait to get there.
I have wanted to see that band for years. I can’t wait for the concert!
There is a different and more literal meaning.
The appointment is in one hour. I can’t wait for him to get here. So I’m leaving now.
Another usage.
I can’t wait forever.
This means that you can wait, but not for a long time.
Thank you so much, NearlyNapping 
Very nice.