"Ahu" are stone platforms on which many moai sit. There are 313 known ahu and 125 of these carry moai. The biggest, Ahu Tongariki is 220 m (720 ft), and had the most (15) and tallest moai.
There is no age, height, or weight requirement to skate. It is good exercise no matter what your age is. If you want to be competitive, most start young. But, I practice with many adult competitors.