eldest

hijo mayor

Refers to the male child in a family who was born first.

el hijo que nació primero o es el mayor

hijo/a mayor

Refers to the child in a family who was born first, regardless of gender.

Se refiere al hijo o hija de una familia que nació primero, sin distinción de género.

Refers to the female child in a family who was born first.

Refers to the male child in a family who was born first.

hermano/a mayor (el/la mayor de todos)

Refers to the one among brothers and sisters who was born first.

Se refiere al hermano o hermana que es el/la mayor de la familia.