I would say that is true, but I think his body is more athletic than just about anyone else we've ever seen pick up a racket and therefore more efficient at coping with the demands made on it. Look at Nadal who has a visibly lopsided body (arms!) compared to Novak who looks like his body was sculpted without an single flaw to be perfectly efficient at playing baseline tennis. He moves as well today at 33 as he did when he was 25, which is not something you can still say for Federer or Nadal who have had to change their games as they have got older.
He also pays more attention to his diet than most others, something he has been doing for a long time now. It will certainly help prolong his career, same as it has done for other top athletes like Lewis Hamilton.