Thirty-nine is not an age known for athletic achievement.
By the time an athlete is 39 years old, they are generally either winding down their careers or already comfortably ensconced in retirement. It's the time when your reflexes start slowing down, when you begin to struggle against fighters who you would've blown right through a few years ago.
It's when you start thinking about getting a broadcasting gig or devoting more time to running your gym or signing to fight for Bellator.
There are exceptions to the rule, of course. The ageless Randy Couture comes to mind.