Guo began learning the art form in primary school. The 35-year-old kept practicing it at least once a week.
He sees the writing process as a way to talk with himself, through which he says he is enlightened and able to find his own life philosophy.
For Zhou Jinsheng, writing calligraphy is more like a kind of sports activity. The 75-year-old has been writing on ground with a big-size brush in Beijing's parks for 10 years.
He needs no paper and ink, just a 1-meter-long brush he makes and a bucket of water. The ground is his paper and the water is his ink. When the weather is good, he goes to a park near his home and writes on the ground. Always, his characters draw some passersby.
"Writing on the ground is very environmentally friendly. It requires the balance of my limbs and waist. Every time I finish my practice, I feel like finishing a set of tai chi exercises," says Zhou, whose peers prefer tai chi, a slow form of exercise popular among old people.
Zhou looks much younger than his age and enjoys good health. He attributes it to his longtime practice of using big brushes to write on the ground.
"It's not only good for my body, but also for my mind," says Zhou.