If they're between 12 and 18 (in mind if not in body) then they are eligible. However, there are handicaps for characters with supernatural powers. Basically, their powers are 'locked' until the character is able to find a 'key,' a small item that they need to keep on their person to utilize their abilities.

This is explained in the rules post on the community, as well as other specific details.

If you think that a bigger handicap is needed, feel free to make suggestions!