I do not think that description is accurate, but I do believe there are big differences in people due to birth order. I have also realized that most of my close friends are first borns. I really tend to NOT get along with only children. One of my roommates was an only and she pissed me off all the time! My husband is also a first born and we are super stubborn
Keep in mind that age difference matters. For instance, you can be technically the baby, but if you are 5 or more years younger than the others, you will probably be more of an only child. Or if you are the second child out of many but the first child is much older, you might be more of a first born personality.