Males can mate every year. Females taking 4 years is a bit frustrating for them. So males fight vigorously over receptive females, and often show combat scars. The juveniles mature slowly over 9 to 13 years, and Tuataras live for 60 to 100 years. The sex of Tuataras is decided by soil temperature around the eggs.
Warm soil causes males, cool soil leads to females.
Most animals have gender decided by x and y chromosomes. Third eye Tuataras have three eyes, but the third eye is only tiny. It grows on top of the head, under the skin in adults, and has a retina with nerve connection to the pineal. The amount of light falling on the third eye may trigger these biological cycles.