Ji he was also. Namikaze Minato is Jiraiya's apprentice. Why is it the fifth generation, but the fourth generation?

Because when choosing four generations, Gang Shou and Jiraiya were not in the village, but between Namikaze Minato and orochimaru, the three generations thought Namikaze Minato was more suitable, because he saw orochimaru's ambition, and Namikaze Minato inherited Jiraiya's will of fire. Compared with Feng Boshui, the most suitable candidate for the five generations came uninvited after the death of the three generations, but he was improper and recommended the master, so the master became the fifth generation.