I do not think we can live up to our ancestor's standards.
I couldn't disagree more. We are perfectly capable to living up to our ancestors physical conditions, just as they were capable of sinking to our lows of gluttony and sloth.
Ancient soldiers and athletes did not have access to the vast collection of knowledge we now have on the human body and how it grows. They also did not have access to the great variety of nutrition we enjoy today. The only thing working against us is, as always, ourselves. You must not allow yourself to get addicted to modern conveniences.
Physical fitness is a matter of discipline and will power. This has always been the case, and will always be.