From
刘禹锡 Tang poem 《
酬乐天咏老见示》 (In Reply to Bai Juyi's Verse on Old Age):
莫道桑榆晚,为霞尚满天。 - 'Do not say the mulberry-and-elm hour is late; its afterglow still fills the sky.'
桑榆 (the mulberry and elm trees where the setting sun rests) was a classical metaphor for the final stage of life.