Taleb is saying that the surgeon being a surgeon itself is the measure of his quality in the same manner that Lindy prescribes that age is a marker for stabilit

Taleb is saying that the surgeon being a surgeon itself is the measure of his quality in the same manner that Lindy prescribes that age is a marker for stability. The fact that he continues to be a surgeon provides you with information about his fitness as a surgeon. In the face of poor appearance, his existence as a surgeon provides you information about his quality.