"For the first time in forever"

This is the part of the lyrics from the movie "Frozen", you know, I love this movie!
It is translated to "うまれてはじめて" in Japanese language.
How come?

Example:
"For the first time in 20 years" →20年ぶりに(20年間で初めて)
I can understand what this means.

I know the word "forever" means 永遠 in Japanese, it means for a long long time, no end, right? Then why is it "for the first time in forever" can be translated to "うまれてはじめて"?

Note: Disney movies often try to make the song sound as good as possible while following the tune. The Japanese word for forever may have sounded akward here, either that or they were trying to make it rhyme. Either way, translations in any language usually are not perfect!