Establishing at thirty: refers to the fact that a person should have his or her own career at the age of thirty. The ancient saying "three establishments" refers to establishing one's morality, words and trust;

Do not be confused at forty: refers to At the age of forty, a person has a mature perspective on people and things in the world, and is no longer confused;

Knowing destiny at fifty: refers to the fact that when a person reaches the age of fifty, his destiny in this life is basically determined; My physical condition and thinking have begun to decline, and I have passed the best period for my career. Life has basically been fixed, and there will be no major developments.

This is my understanding, I wonder if you are satisfied with it.