expression, noun
heyday; prime; height of one's prosperity
A set phrase meaning the period when someone or something is at the peak of success, influence, or happiness. Often used in the pattern 〜の我が世の春 or 〜は我が世の春だ.
彼は今が我が世の春だと感じている。
He feels that now is the prime of his life.
あの歌
That singer's heyday was the 90s.