Emperor Taizong's name means to help the world and people. He can be emperor as soon as he is born?

The question you mentioned is recorded in both the old and new Tang books, and it is almost the same. Now I will extract it for you.

Book of Old Tang Dynasty: When Qi Lin was Emperor Taizong, he was four years old. Some scholars say that they are kind to each other and praise Gaozu for saying, "You are a noble person and you have a precious son." When he met Taizong, he said, "The posture of dragons and phoenixes, the posture of heaven and the posture of the sun will surely help the people at the age of twenty." Gaozu was afraid of his words, so he would kill him and suddenly lost his position, because he was famous for adopting the meaning of "helping the world and the people".

"New Tang Book": When Fang was four years old, a scholar praised Gao Zu: "When the public is in the law, the nobles are also there, and there must be a noble son." Seeing Emperor Taizong, he said, "The appearance of dragons and phoenixes is the face of heaven and the face of the sun, and the number of its crowns will surely help the people all over the world." The scholar has resigned, and the great-grandfather is afraid of his words, which makes people chase after him. He doesn't know where to go and thinks he is a god. It is based on its language and is called Shimin.

However, as the fortune teller said, so-and-so will do great things in the future. These are the childhood records of the rulers of past dynasties. It was invented by the rulers to strengthen their rule. The name Shimin should be Tang Yuan's expectation for his son, not necessarily an emperor, but also a court official.