Amphibian life history strategies can vary across broad geographic patterns, which have been explained, at least in part, by how development, growth, maintenance, and reproduction respond to temperature. However, there is a dearth of information regarding life history traits and their variation among populations for many amphibian species, which prevents assessment of these broad patterns among species. Therefore, we used museum specimens to assess the variation in reproductive condition of Plethodon montanus across its range and used skeletochronology at five populations along an elevational gradient to determine the elevational variation in age, growth rate, and asymptotic size. We found that body size and temperature seasonality best explained the variation in the presence of eggs and a mental gland, whereas body size alone best explained the presence of enlarged pigmented testes. We also found that longevity in P. montanus is at least 12 years with higher elevations having a higher proportion of older individuals compared to lower elevations and that size was a better explanation of reproductive condition than age across the elevation. Our results further demonstrate the importance of body size for amphibian life history traits and the utility of museum specimens to estimate these traits. Variation in reproductive condition across the range of P. montanus is likely the result of variation in growing season length. Lastly, we found evidence suggesting asymptotic size and growth rates may have changed over the last half century, which would ultimately affect fertility and other life history traits and warrants future studies.