Exactly. Though many of us judokas on here compete, the people who compete at the very top have often spent their lives becoming really proficient attaining a true "mastery," starting when they are small children and usually peaking between the ages of 22-30.
While someone might make black belt, in judo, this doesn't necessarily translate into "mastery." For most Judo schools, the bb is considered the beginning, rather than the end of a journey. It doesn't apply any total mastery, especially at the shodan level.
So, excluding belts, let's look at the Olympics, each country's best, as an indicator of a level of mastery. Most of them have spent their entire lives training, often almost every day (this is certainly the case in Japan).
In order to reach a true level of mastery, in judo and wrestling, despite some exceptions, generally I think people have to start very, very, young and train intensely until they are around 22-30 because after that teh body starts to go down hill. It is a short window of time and a level that most of us will never reach.