Chinese Astrology. According to it, the year of birth does not only tell only your age but also indicates a certain phase or aspect of sixty year circle of time. 

In Chinese system of astrology, each year begins early in the calendar year on a new moon and relates to one of the twelve animals. Their qualities "animate" the year and color it with their distinct natures. 

Therefore you may find yourself born in the year of Rat or a horse or even a dragon as the lore says it. People born in a particular animal year share certain common traits in the same manner as people born in common zodiac do. Check your Chinese Sign, Chinese Type and Chinese Element here. Also check Your Sign's Detail