Birth order and dating
“This has been studied very well from a psychological standpoint.
The most successful marriages are those where the oldest sister of brothers marries the youngest brother of sisters.” Think about it.
Firstborns bask in their parents' presence, which may explain why they sometimes act like mini-adults.
"It's definitely a sibling love/hate thing."The Grown-Up Firstborn As firstborns grow older, their traits are not necessarily lost.
Kevin Leman, a psychologist who has studied birth order since 1967 and author of (Revell).