2 sentences for 老大 (lǎo​dà — eldest child)

1. 他在家里排行老大，下面还有两个妹妹。

   tā zài jiā​lǐ pái​háng lǎo​dà, xià​miàn hái yǒu liǎng gè mèi​mei.

   He is the eldest child in the family and has two younger sisters.

   Source: Dong Chinese Dictionary

2. 他在家里排行老大，所以从小就非常有责任心。

   tā zài jiā​lǐ pái​háng lǎo​dà, suǒ​yǐ cóng xiǎo jiù fēi​cháng yǒu zé​rèn​xīn.

   He is the eldest child in his family, so he has been very responsible since he was young.

   Source: Dong Chinese Dictionary