Does AGE determine whether or not a fighter is "past his best?"

Age of the current Ring P4P 10
1. Pacquiao (29) 2 weeks from 30
2. Marquez (35)
3. Calzaghe (36)
4. Hopkins (43)
5. Vazquez (30)
6. Margarito (30)
7. RMarquez (33)
8. Cotto (27)
9. Calderon (33)
10. Hatton (30)

These are the 10 BEST fighters in the WORLD (according to The Ring). Only Cotto is in his 20s.

Surely ANY win against a fighter rated TOP 10 in the world CAN NOT be downplayed, right? Yet fans/writers make excuses for fighters losses, because of old AGE, all the time.

Isn't this a contradiction?

Thoughts?