Using the lines of arrested growth (LAGs), we estimated the age structure of a breeding population and individual ages at sexual maturity of a salamander, Hynobius lichenatus, from Sendai, northeastern Japan. No significant sexual differences were detected in either the age structure or the age at maturity, and the breeding individuals ranged from 5 to 14 yrs old, while the age of their maturation ranged from 3 to 7 yrs old. Reasons for this difference in minimal ages remain to be studied. There was no significant correlation between the age and the body size of the salamanders. Hynobius lichenatus does not differ from its close relative H. tokyoensis from Tokyo in age structure, but mature significantly later, with a longer life, than H. tokyoensis from Chiba. These findings suggest that the age structure of these salamander populations is affected at most partially by temperature conditions, and more strongly by other environmental, ecological, or phylogenetic factors.