Responses
By minister, do you refer to Rong Tian? If he's who you're refering to, then you are incorrect. Rong Tian is actually around 18 while Feng Ming is 19 when he died.
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Rong Tian is at least one or two years older than Feng Ming since he acted as a Regent King and at the time Feng Ming/An He wasn't of age yet to be crowned King.
I don't think the minister is the same age, in that position he would have to be much older at least late 20's. Is that book in print?