noun · the first-born or eldest child in a family

他在家里排行老大，下面还有两个妹妹。

noun · to a great degree; very or extremely (often used with fixed negative expressions)

听到这个消息，他心里老大不高兴。

noun · leader of a group, boss, captain of a boat, or head of a criminal gang

他是我们公司的老大，所有大事都由他决定。

noun · advanced age or the state of being old

少壮不努力，老大徒伤悲。