Don't count out Robert Guerrero's chances of pulling off a historic upset over the undefeated Floyd Mayweather when the two meet on May 4.
Mayweather just turned 36, and Father Time hasn't lost a bout yet.
While fighters like Juan Manuel Marquez, 39, and Bernard Hopkins, 48, have shown they can push back the career-ending effects of aging, there are plenty of other red flags here for Mayweather.
First and foremost is his last bout with Miguel Cotto.
While Mayweather emerged victorious, he was far more battered than after the typical fight for the elusive champion. Against Cotto, Mayweather endured through a bloodied nose, split lip and numerous big shots.
Mayweather attributed his struggles to his desire to give the fans a good show.
While that is very thoughtful of Money, it is also hard to believe. Especially when Money did not appear to have the same quickness and fluidity of subtle movement that has made him one of the greatest defensive boxers the sport has ever seen.
The more realistic theory behind Mayweather being on the receiving end of so many big shots is that he is slowing down to the speed of us mere mortals.
The fact that Mayweather's greatness has stemmed so much from his speed and defense makes him especially vulnerable to the effects of aging—speed is going to be stripped sooner than power.
This is also highlighted by history.
Roy Jones Jr., who also relied heavily on tremendous quickness, was drilled to the canvas by Antonio Tarver at the age of 35. The fight was stopped and it was the first loss for Jones that didn't come via a disqualification.
Let's look at another similar fighter: Sugar Ray Leonard. At age 34, Leonard was expected to dominate Terry Norris. Instead, Leonard appeared as a slower version of himself and was dominated en route to a unanimous-decision loss.
Now, this doesn't mean Guerrero is going to wipe the canvas with Mayweather. He will still be a quick fighter who throws accurate punches. However, he is also far more vulnerable to the kind of knockout blow that could end his time as one of the sport's dominating figures.