I'm sorry that my little daughter is so ignorant. What does "7-year-old luck" mean? thank you

Seven-year-old luck means that you start the first step at the age of seven, the second step at the age of seventeen, once every ten years, and so on.

This is a term in eight-character fortune telling. It comes from your month and is used to combine the annual expenditure with your horoscope, so as to calculate your fate every year between the ages of seven and seventeen.