I had the best time and the best age in that youth. Personally, I think the flip here is a magnificent performance, indicating that the author is in a certain peak state. "The overthrow of youth" means "that good era came to the author", just like the situation when the flood poured down. Expressed the author's "youth" and "youth". But his "madness" and "conceit" are indeed a kind of fighting spirit and a kind of confidence in himself. Also express the author's vision for a better future!