Holding back. Try replacing the word "stuttering" with "holding back". I "stutter" the worst when I talk to people older than me and during those moments I ask myself why am I "holding back" instead of "why am I stuttering" and then I remind myself why I'm holding back. Most people usually don't stutter when they talk to children or animals it's because they feel they are in control and have the power of authority whereas if you talk to another adult, you give them the power of authority. It has to do with our perspective of adults when we were a child. It's our natural instinct and survival as a child to be liked by adults.