It must be a coincidence that both Liu Bei and Zhuge Liang gave birth to sons at the age of 46. They can't have discussed it beforehand. There are several reasons why they can't have children. First, Liu Bei was a soldier in his early years and often lost his wife when he was defeated. Therefore, the time spent with his wife is limited, and the probability of having a son is naturally low. Second, Zhuge Liang's wife Huang is ugly, so it is possible that Zhuge Liang has been close to her less often, so it is impossible to have a son. Third, it is possible that they were the first to have a daughter, but this matter is not recorded in the official history and it is impossible to talk about it. However, many people do have daughters one after another, but they don't have sons. Perhaps Liu Bei and Zhuge Liang had many daughters, but they gave birth to their first son at the age of 46.