The eldest child in a family, or individual in a group.
"As the eldest sibling, Maya always took on the responsibility of looking after her younger brothers and sisters."
superlative form of old: most old; greatest in age or seniority.
"As the eldest at the table, I got to see my hole cards before anyone else could make their opening bet."
(of a player) Receiving cards from the dealer first, before any other players.