The Old Man must be refering to Dax. Not sure if it's Ezri or a new host. Since Dax was referenced as a 'he' this might mean that Ezri has died and the Dax symbiont has a new host. OR C'thal might've been a friend of Kurzon. I'm betting it's the latter.
That may well be true... We could see an offspring of Ezri (And Dr Bashir, I presume)? There are other examples of famous offspring in-game. (Spoilers : Kirayoshi at Memory Alpha, Gul Dukat's daughter etc.)