The years of age of Mengzi 孟子 when he had the audience with King Hui of Liang 梁惠王 may seem trivial; however, after an attempt to verify the date in question in his seminal work Xian Qin zhuzi xinian 先秦諸子繫年 (A Chronology of the Pre-Qin Masters), historian Qian Mu 錢穆 (1895-1990) postulated that Mengzi visited the state of Qi during the reign of King Wei, and suggested a series of related hypotheses on the ages of Gaozi 告子, Kuang Zhang 匡章, Song Xing 宋鈃, Zhuang Zhou 莊周, Hui Shi 惠施 and Bai Gui 白圭, and their respective years of travelling around and serving at the court of various warring states. Hence, such dating is not to be treated lightly. Although some scholars have refuted Qian's propositions, they have not provided solid evidences with regards to how old Mengzi was when he first met the King of Liang. This paper tries to tackle this very question and suggests some alternatives to the dates related to other pre-Qin Masters. I conclude that Mengzi was in his fifties when he had the audience with King Hui of Liang, meaning Mengzi was probably younger than Song Xing, and perhaps even Zhuang Zhou.