This is an old saying, which means that after a person reaches the age of thirty, it is difficult to learn a craft or change careers to learn a new craft, because at this time, you basically have a family and children. There are constraints and worries when learning new things, and age is also there. People's energy and motivation are not as strong as when they were young.

As for people passing noon after forty days, it means that when a person reaches the age of 40, it is like passing noon in a day. After noon, the day passes quickly, just like a week. , after Wednesday, a week passes quickly, a month passes quickly after the 15th, and a month passes quickly. So here it is said that when they are over 40 years old, people will grow old quickly. To exaggerate, they will be buried before their death. Not far away.

I think these two sentences mean that people should cherish the present, seize the time to do what they want to do, don’t leave any regrets, don’t waste your time, time and age will not wait for us