From a mathematical model of aging are deduced three unit-free numbers. It is possible to calculate a critical value of the number beta t, where beta means the aging rate and t the chronological age of the organism. If beta t is greater than 1.84, then the theoretical life span is reached. Using an iteration method another unit-free number, namely, the quotient x of the growth rate and the aging rate beta is calculated to x = 4.5.