Mammoths continued growing during adulthood, as do other elephants. Males grew until age 40, and females until age 25. Mammoths may have had gestation periods of 21–22 months, like those of modern elephants. Columbian mammoths had six sets of molars in the course of a lifetime. At 6–12 months, the second set of molars would erupt, with the first set worn out at 18 months of age. The third set of molars lasted for 10 years, and this process was repeated until the sixth set emerged at 30 years of age. When the last set of molars wore out, the animal would be unable to chew, and would die of starvation.