Right, and that disadvantage is being lessened as athletes are finding more and more ways to prolong their physical peaks, recover from serious injuries, etc etc. My point is that advantage younger players used to have isn't as big anymore.
As for Murray, well you may well be right lol. I do agree with you that the younger generation could work a lot harder.
I'll concede that, to a point but the difference is nowhere near significant enough to counter the benefits of youth in regards to the large advantages it holds in other elements of physical fitness.
Today we have 3 players in their mid-twenties atop the rankings and I believe that when they're 'fit', they will surpass the general past-norm of players' standards in their early 30's but only because of their reliance and dedication to their physical fitness. You can't come to an accurate conclusion unless you set everyone on the exact same training regime, diet and lifestyle to conclude whether A has a more genetic advantage than B or C is only fitter than D because... etc.
I take Ferrer as a perfect example of a player who has continued to work hard physically and he's reaping the rewards. Ferrer is also an exception in the way that he has maintained much of his agility and I'd say all if not more speed horizontally. It's a credit to himself and those around him and a wake-up call to those youngsters who are happy enough collecting pay cheques and believing that their time will come (possibly through the departure of others) performing and training as they do currently.