Old Man

From Memory Alpha, the free Star Trek reference.

"Old Man" was a nickname given to Jadzia Dax (and later Ezri Dax) by Benjamin Sisko, in reference to their previous host, Curzon Dax. (DS9: "Emissary")

When Jadzia decided to stay on Meridian, which would have meant the two would not see each other for sixty years, Jadzia joked that she could call Sisko "old man" when they would see each other again. (DS9: "Meridian")

Sisko also called Yedrin Dax "Old Man" when they met in 2373. (DS9: "Children of Time")