And yet things like City Hunter being blooded or older or more experienced aren't taken from any evidence in the movies. It's fan speculation.
Does the Predator 2 book or comics lend insight on his age? Are there interviews with Winston, Kevin Peter Hall, or Stephen Hopkins?
That would be where one could ascertain the age of City Hunter, in the intent of the director, how Kevin was told to act in comparison to his Jungle Hunter performance.