Not even talking of records, finishing the year at number 1 at 31 years old in a very physical era and with such competitors as Djokovic, Nadal
and Murray, even though they're not at their best (although in their prime years
), would be just incredible and would fully achieve the "back to youth" story at an old age which this year looks like for him.
How many prime years does Nadal have? Clay king was already a physical beast at 18/19 years! Nobody would say at that time "He will probably be in his physical prime when he is about 26" His physical prime was more likely to happen at around 20-24 years and it probably did.