Meaning of "In his prime"

Ri-Jeu-Si-Jeol

In his prime리즈시절#덕질/팬덤#밈/유행어2010s Meme

Originating from the lamentations of soccer fans regarding "Leeds United," this phrase refers to a situation where it seems unlikely that the glorious heyday (or the glory of that time) once enjoyed by an individual or group will ever return.

"Even now, he recalls his past achievements and speaks of his heyday with a tone that is less pride than self-deprecation."