我若长发及腰你定白发飘飘
[wŏ ruò zhăng fā jí yāo nĭ dìng bái fā piāo piāo]
Translating to 'If I have long hair reaching my waist, then surely you will have gray hair flying in the wind,' this is a poetic expression implying a shared lifetime and aging together with someone cherished.