most geckos become sexually mature just over a year old. to tell you the time it takes to reach full size, the crested averages at around 8 to 10, my youngest one in this range is just over a year and a quarter old, but at the same time i have another that was born days later, which is just hitting 7. they will reach their full size by the time theyre 1.5 to 2 years old.