I wouldn't say it's a sign he improved, unless it's implied or shown that he got more powerful. It was said Whitebeard reached his Prime in his late 30s. After that he also clashed with Roger several times and ruled as a Yonko for decades. Kaido's fights were merely suicide attempts.
No, I would say that it is a sign of improvement, defeating powerful pirates he managed to become an emperor, this phrase itself says that he had matured and he went up.
Because if we are going to take the bet seriously, I would say that you have already lost.
"Oden said, get stronger while you still can."
This is the VIZ translation for my language.
You said he was at AUGE right? Oden disagrees.