It is not solely about weight. It is the ratio between weight and surface area. Surface area tends to go as the square of the size whereas mass tends to go as t

It is not solely about weight. It is the ratio between weight and surface area. Surface area tends to go as the square of the size whereas mass tends to go as the cube. For objects of the same density (all people are about the same), smaller and thus lighter ones have a greater surface area to mass ratio, and thus a lower terminal velocity.