What does the idiom "people are old" mean?

Whether it is calligraphy or painting, it takes time to reach a high level, just like stewing an old hen. Without time and heat, the final taste will not be in place. Nowadays, many people who engage in painting and calligraphy dare to call themselves home at a young age, just like stewing an old hen in a pressure cooker. It's rotten, but it has no taste, or it doesn't taste enough. Only after a long time, people get old, which means extensive knowledge, rich experience, higher cultivation and profound morality. Only in this realm or artistic conception can people and books grow old.