What's more impressive

This. :deal

 

The advantage I guess the best word here is advantage that youngest has, is that it's would be harder to acomplish. When Wilfred Benitez beat Antonio Cervantes, he was about 17 and a half years old. Consider tjhe fact that it takes most boxers 3 to 4 years to become champions, even the best ones. This means you have to turn pro at 13 or 14 at the oldest. Next because you don't have a long amature career. You need to be from some place that would alow someone to become a pro at such a young age. I think in Mexico they often start at 15, but that might be too late. I have herd that in Thailand Muy-Thi boxers start very young. I remember that Clarence (Bones) Adams was 15 when he turned pro.
What I'm trying to get at is that it would be next to imposible to win a championship so young. Not only do you need the talent/skill/abilities to do so, but you also need the right circumstances to do it.

As far as being the oldest. These days athletes are able to prolong their careers. It is likely that baring a major injury every champion and contender today can fight at the top level of the sport into their 40's. I don't think we are too far from a 50 year old champion. It is at least more likely to happen than a 16 year old one is.

 

Youngest, in general.

Old guys have the benefit of experience and years developing their skills.

Young guys usually only have athleticism coupled with skills that are still being developed.

Benitez becoming a world champion at 17 is one of the most amazing things in the history of boxing. Most fighters are still trying to conquer the Golden Gloves at that age. Patterson winning the title at age 21 is a phenomenal accomplishment for a heavyweight.

 

Depends on the competition.

Benitez beat a hall of famer with his high school class in attendance.
Hopkins beat Jean Pascal.