Does Anyone Else Talk Or Act Like A Child?

I'm in my early thirties and I feel like I have the mentality of a child or teenager. I feel like a child in an adult body. I can't seem to figure out why I'll talk like a child. My voice gets high-pitched and soft. My case manager noticed that I talk like a child or I'll talk like a mature adult and wants me to talk to her like an adult. She is unaware that I have borderline personality disorder. Does anyone experience acting or talking like a child as well? Is there a logical explanation?