A contoured seat form includes a lower support surface on which a user's legs and buttocks are supported, the lower support surface including a forward edge having: i) a pair of primary leg support surfaces extending inwardly from side edges of the forward edge; and ii) a pair of indent surfaces, each extending backwardly from the leg support surfaces. At least one leg indentation is formed into which a smaller rider's leg or legs can fit. A back support surface by which a rider's back is supported includes a pair of contoured protrusions that extend forwardly therefrom, the pair of contoured protrusions defining a torso indentation therebetween, the torso indentation being sized such that a smaller rider's torso will fit between the pair of protrusions while a larger rider's torso will be prevented from entering the torso indentation by the contoured protrusions.