Northern sea otters (Enhydra lutris kenyoni) are experiencing rapid population growth and expansion in Southeast Alaska. Fluctuations in population density can produce profound changes in ecological constraints, influencing growth and sexual maturity of animals in a population, and can transform the ecology of newly populated ecosystems. Using morphometric measurements and reproductive tracts collected from 40 sea otters by an Alaska Native subsistence hunter, we evaluated growth rates and age at sexual maturity of male sea otters near Gustavus, Alaska. Standard length of mature otters (asymptotic size = 148.2 ± 2.9 cm [SE]) was greater than previous studies in Alaska. At puberty, mean seminiferous tubule diameter, baculum length, and testes mass increased abruptly at 130 cm body length. Animals in this study reached sexual maturity earlier than previous studies, at age 3–4 years. Baculum length increased rapidly at sexual maturity and was a good indication of maturity status (< 14 cm = immature). Increased body size and lower age of sexual maturity suggests resources are not limiting growth and maturation of sea otters near Gustavus, Alaska.