I had a HUGE axolotl! 💞 On average, an axolotl will grow to around 9 to 12 inches long, though some individuals have been known to stretch up to 18 inches in rare cases. Their size depends on genetics, diet, and living conditions. Unlike many other aquatic pets, axolotls keep growing slowly throughout their lives, though they reach full adult size within about 18 to 24 months. A larger axolotl means a bigger appetite and the need for a properly sized tank, usually at least 20 gallons for one ad