Manny fought very well for a 42 year old fighting at least 2 divisions higher than he should be. Ugas looked like King Ghidorah against tiny Manny. When Pac was younger, size didn't matter as much. He fought hard, but was up against a guy whose reach allowed him to tag Manny from a mile away.
it's nothing but a number for what you can do if your body is fit and healthy, but depending on the activity, it can greatly affect how well you can do it.