Everyone has their prime age. Different individuals reach their prime at different ages. In the world of competitive sports, the career span of an athlete is heavily dependent on their body. For boxing, or any other sports with a lot of wear and tear, a person’s prime is short lived.
As a person ages, their body starts to degrade. This is why old boxers are often called “shot”. Though once extremely skilled and athletic, they have degraded to a point where the younger generation can now beat them, despite the experience gap.