When asked what ages quickly, he replied, “Gratitude.”

[ἐρωτηθεὶς τί γηράσκει ταχύ, “χάρις,” ἔφη.]

Aristotle (384-322 BC) Greek philosopher

Attributed in Diogenes Laërtius, Lives and Opinions of Eminent Philosophers [Vitae Philosophorum], Book 5, sec. 18 [tr. Mensch (2018)]
    (Source)

(Source (Greek)). Alternate translations:

Once he was asked what grew old most speedily, and he replied, “Gratitude.”
[tr. Yonge (1853), sec. 11]

Being asked, "What is it that soon grows old?" he answered, "Gratitude."
[tr. Hicks (1925)]

When he was asked what grows old quickly, he said "thanks."
[tr. @sentantiq (2016)]