This is true. I am a middle born and that is kinda true about me. same for my bro another middle born. and my oldersister first born. the only one that is wrong is my little sister "last born" she isn't like that really.
I am not an introvert but I love and respect a great many people who are. I wish more people would understand what it means to be an introvert - maybe you are and you don't even realise. Introversion does not equal shyness.