Fedor is 33...of course he would be slowing down. Most athletes start to lose a step once they hit 30. Late 20s early 30s is usually what they call an athletes "prime."
It's a step below their peak athleticism, but they've reached a mental level where the aggregate of their experiences allow them to read their opponent and know what to do to counter, and take advantage of the situation. As the years roll by, they can still read their opponent and know what they need to do, it's just their body won't respond anymore. ( That's when you retire and become a coach )