Oxidative stress has been reported to increase with aging, and although several age-related changes in redox parameters have been described, none of them have been verified as markers of the rate of aging and life span. Therefore, antioxidant (catalase, glutathione peroxidase, reductase activities, and reduced glutathione) and oxidant (oxidized glutathione, basal superoxide anion, and malondialdehyde concentrations) parameters were studied in whole blood cells from humans divided into different age groups (adult, mature, older adult, nonagenarian, and centenarian) in a cross-sectional study. Moreover, the same parameters were investigated in peritoneal leukocytes of mice at the analogous human ages (adult, mature, old, very old, and long-lived) in a longitudinal study as well as in adult prematurely aging mice. The results reveal that the age-related alterations of these markers are similar in humans and mice, with decreased antioxidants and increased oxidants in old participants, whereas long-lived individuals show similar values to those in adults. In addition, adult prematurely aging mice showed similar values to those in chronologically old mice and had a shorter life span than nonprematurely aging mice. Thus, these parameters could be proposed as markers of the rate of aging and used to ascertain biological age in humans.