You’re the oldest sibling
Being the oldest sibling has several advantages, like being able to tell your younger brothers and sisters what to do. After analyzing soldiers’ IQ tests, Norwegian researchers found that oldest children had an average IQ of 103. Second-born kids had an average IQ of 100, while the babies of the family had an average IQ of 99.
Oldest children have a unique relationship with their parents and younger siblings, which may explain the difference.