i had often wondered about this as i have a lisp, but none of my family or my three children have,so it is not something one would learn as i taught my three children to speak,ha ha...........as a child i was often teased by other children but as i grew older no one really mentions it unless the subject is brought up and then the usual daffy duck saying comes from some one "a ssssixthpenny bus fare please " but i can laugh about it now.......
well i can tell you right now lisps have nothing to do with the length of your tounge. If anything, it may be because the tounge is too long. often, with a frontal lisp, the problem is the tounge pushing out from the teeth and causing your s and z to sound like th. or with a lateral lisp, the tounge is inbetween the teeth on the side causing air to blow between your cheeks giving the person difficulty with s, z, j, and sh causing distorted and jumpy speech.