Infantilism vs Being Infantile

So I knew this girl from Texas and she thinks bed wetting is hilarious... She has infantilism... which in no way is the same thing as being infantile, in fact, she seems to lack any capacity for being infantile. The redeeming question to ask is: Is there any difference between people who have infantilism and people who choose not to be infantile? I can determine no difference whatsoever. Being infantile is a rational choice one can make for one's own sake... Choosing not to be infantile implies that it doesn't matter to you if no one can tell the difference between you and a person who has infantilism.