Which joke does Jiang Taigong become the prime minister at eighty years old?

From "The List of Heroes of the Gods".

Before King Wen of Zhou Dynasty Jichang went out hunting, he got a divination. The hexagram predicted that the thing he was going to hunt today was not a wild bird of prey, but a wise man who could assist him in achieving world hegemony.

Then Ji Chang passed by the Weishui River and heard that there was a strange man in the mountains. Others kept silent while fishing, for fear of scaring the fish. However, this strange man Jiang Ziya often sang a song in his mouth while fishing, and it seemed that he did not say a word. It’s like not worrying about scaring the fish away. The fishermen around him were laughing at Jiang Ziya for not knowing how to fish: "You will never catch a fish in a hundred years." Jiang Ziya responded by saying that he was not here to fish, but only to catch princes. What's even more surprising is that Jiang Ziya's fishhook is also unusual. His fishhook is as vertical as a pen, and he never puts any bait on it. The fishhook was not placed in the water, more than three feet above the water.

After hearing this, King Wen of Zhou immediately understood his ambition and appreciated his talent. He personally pulled the cart for 800 steps and asked to return to the palace to worship him as the Grand Master. This led to the rule of the Western Zhou Dynasty and the Eastern Zhou Dynasty that lasted for 800 years combined. Extended information

After Jiang Ziya granted the title of Qi and founded the country, he spent a lot of time in Haojing as the "Grand Master" of the Zhou Dynasty's central government, assisting his grandson King Ji Song of Zhou Cheng and great-grandson King Jizhao of Zhou Kang. His eldest son, Duke Ding of Qi, Jiang Ji, did not come to Linzi to govern Qi. Instead, he had been serving as Huben in Haojing, commanding the palace garrison.

For more than thirty years after the founding of Qi State, Yingqiu was basically guarded by Qiu Mugong, the third son of Jiang Taigong. During the reign of King Cheng, Uncle Guan, Uncle Cai, and Uncle Huo were involved in the "Three Prison Rebellions". Huaiyi, Xuyi, and the "Five Marquises of Yindong" rebelled against the Zhou Dynasty. Jiang Taigong and his son assisted Zhou Gongdan, either sitting in Kyoto and strategizing; The troops marched eastward and charged into battle; or they responded from left to right and attacked from east to west, quickly quelling the rebellion and achieving great military exploits for the second An Zhou Dynasty.

Later, King Cheng of Zhou passed away, and Jiang Ziya and his son accepted King Cheng Tuogu’s order and took on the important task of assisting the prince. Later, they worked with the ministers to support the prince Ji Zhao to ascend the throne?, known in history as King Kang of Zhou.

Baidu Encyclopedia-Jiang Ziya