There is absolutely no way that even the most precocious eleven year old could pass as a sixteen year old, still less eighteen, in any serious conversation. They just don’t understand things in the same way as adults.
Simple but famous example - get them to consider a starving man stealing bread to feed his family. They’ll all claim it is wrong (except for the sociopathic bastards that so many of the child “geniuses” turn out to be, who won’t even understand that concept)… they just don’t get shades of grey.