Given Mr Lua’s age of 30, to be a Chief Flight Instructor is unbelievable, therefore, I believe the school had been using him as ‘cheap labour’.
It's not so much his age, but the fact that you usually need a minimum of 1000 hours of flight instructing time, and a minimum of 2000 hours TT to be accepted as a chief instructor by the Indonesian DGCA. So if he had more than 2000 TT, then he would have met the CAAS 700 hour minimum requirement to convert his license to the Singapore license.
But agree, that random 700 hours as minimum for conversion to the CAAS license is a ridiculous rule. Why 700 hours? If you ask me, a 700 hour pilot flying in GA is no different from a 200 hour pilot, especially as a flight instructor where you hardly handle the aircraft anyway. You still have the same skill set at 700 hours of GA instructing as you did at 200 hours. So why make up the rule in the first place?