I think you might be mistaken in conflating his age with his athletic prime. An American fighter, who grows up, wrestles in high school, wrestlers in college, maybe trains for a couple years with the Olympic team before delving into MMA. Yeah, that's guy's prime is probably going to come in his early 30's. But these Brazilians that start fighting professionally when they're 17-18 years old, in Chucky Olives' case 20? They've got a fuck ton of miles on the odometer by the time they hit 30. Oliveira has already had 40 fights. If he has another fight or 2 like he did last night, he's going to have a very short reign.
For reference, look at the career arcs of guys like Shogun or Aldo.