Guan, who bogeyed his first hole and quickly slipped to five over par before making a birdie at the seventh, was 107 days younger than his compatriot Lo Shik-Kai at the 2003 Hong Kong Open.
Before the tournament Guan said he was coping with the pressure of being thrust into the spotlight and that it is not affecting his studies.
“I don’t have a problem with school and golf, I am in the top section of my class," he said.
“I don’t take schoolwork with me when I travel. I just work very hard and my grades are high.”
England's Matthew Baldwin set the pace in China with a first-round 65 to finish a shot ahead of a group of six players including Sweden's Fredrik Andersson Hed.
"It was very good today so I am happy with that," Baldwin told the European Tour's website.
"My caddie and I set out this morning with a game play of trying to make 18 pars and take our chances when they came, and it turned out to be one of those days where there were a lot of chances and I managed to take a few of them."
England's Paul Casey finished on four under par, level with former European number one Colin Montgomerie.