Re: What type of boxer ages the best?
Fighters who while they may be somewhat gifted athletically, their main gifts are mental, and technical, neither of these erode with time, and the former arguably gets better.
See - Juan, Hopkins, I think Floyd falls into this category, though he obviously possessed exceptional physical gifts in his youth, to the extent the other two did not. Also of course, the less punishment taken, the better.
Combine their fistic skill with what will generally be a high level of adaptability and you have a recipe for longevity, and other words that almost rhyme.
Pep is another good example