(to live together until the) white hairs of old age (idiom); to live to a ripe old age in conjugal bliss
until death do us part
Definitions (粵典–words.hk)
語句
祝賀語。指結婚之後維持婚姻直至夫妻都滿頭白髮 literally to remain married until the hair of the husband and wife becomes grey; remain happily married until husband and wife are both very old
祝你兩個新婚快樂,白頭到老。
祝你两个新婚快乐,白头到老。
zuk1 nei5 loeng5 go3 san1 fan1 faai3 lok6, baak6 tau4 dou3 lou5. May you two have a happy wedding and remain happily married until you are both very old.