I think that is legitimate question. Congo a country in Africa does not require its citizens to register birth certificates so naturally majority of its citizens do not. Considering Congo was/is affected by wars/crime/instability then we have got a mass number of people moving around with kids who may not have attended school for a few years and their parents do not keep track of a child's age so the child may not even know their own age.
Lets move to another country in Africa like the Cameroon for instance. A country of the home of Siakam and Embiid. This country has been much more stable both politically and economically then the Congo. Their citizens are more likely to register their births as well as their kids more likely to attend schools from a young age and therefore it has a better validity of a track record which is why there hasn't been questions and concerns regarding Siakam or Embiid's age.
The thing with age is that, its true that once you reach the age past 30 your value decreases. However there are no guarantees that your value might even decrease before you reach that age. So in conclusion it was up to Masai to weigh in the factors and make the decision to pull the trigger. The bottom line is that the Raptors want to compete for a championship and have to use that small window to try and close the gap between them and the true elites of the NBA, and I think they made that one small step in the right direction with that trade.