It is not possible to say exactly how much a person should save by what age due to large differences in the American standard of living. A person who has been earning $ 500,000 a year for decades would be disgusted to have to live to old age with $ 30,000 a year.
Conversely, most of us who are currently swinging at $ 50,000 a year or less would be perfectly fine with $ 30,000 a year in retirement to have a safe place to live. Use calculator here to adjust your retirement goals.