The Chinese "xu sui" (age) is an important folk custom in China. It is divided by the Spring Festival (Lunar New Year), while the "zhou sui" (actual age) is divided by one's birthday.
The specific conversion method is as follows: converting "xu sui" to "zhou sui": before the person's birthday, "zhou sui" = "xu sui" - 2; after the person's birthday, "zhou sui" = "xu sui" - 1.
Converting "zhou sui" to "xu sui": before the person's birthday, "xu sui" = "zhou sui" + 2; after the person's birthday, "xu sui" = "zhou sui" + 1.