birthdates is used for fortune-telling and measuring life. If you are too young, it is not suitable for fortune-telling, so parents will not give you the horoscope, for fear that you will go around telling fortune after you know it, which will do harm to your young mind.
When you are old and have rich social experience, you need to use birthdates to guide your life, and then it is suitable for fortune telling. So my parents told you the eight characters.