Anderson Silva and Dan Henderson are 37 and 42 respectively, Couture was also competitive in his early 40s and Lindland remained a top MW into his late 30s. Certain styles and certain fighters age better than others.
These guys are the exceptions to the rule. Most fighters start declining in their early 30s. I would have no problem with a longevity hidden, where the vast majority of fighters would start declining around 28-32, with one or two Randy Coutures in each in-game generation. That kind of longevity would need to be as rare as the TDPW, though.