Randy Couture is an exception to the rule, a unique individual. I used the word age but meant something that comes with age, losing the desire to dominate, to the point where it's hard to justify to oneself maintaining the training regime and lifestyle necessary to be able to compete at the top levels. If someone is so talented that they can do well without it then they are truly well protected from absorbing excessive physical punishment, and endowed with way above average tools, doesn't happen often.
On another note how do you find spearfishing and MMA go together? Diving relaxes me so much I've lost the urge to win a long time ago. When I go train it's because I tell myself it's necessary, I want to know that I'm well protected.