Hong Kong CNN  —  Ding Xueliang spent his early teenage years in China as a fervent believer and practitioner of Chairman Mao Zedong’s revolutionary ideals — but he never imagined those memories would one day be stirred by a sitting US president. In 1966, at just 13 years old, the son of poor farmers became one of Mao’s Red Guards. He joined millions of young people across China to participate in the Cultural Revolution, a decade-long upheaval set off by an aging Mao to reassert his absolute