Kaeya is interesting in Genshin Impact because he’s a Khaenri’an spy, but he grew up with Diluc as a child. They’re about the same age, around 22, give or take a few years. It’s pretty baffling, as he’s a citizen of Khaenri’ah but appears uncursed. He can’t be 500 years old either since nobody is that good at acting as a child, no wonder why players wonder how old Kaeya is in Genshin Impact.
During the events in the Archon Quest in the Chasm, we learn that all the ruined civilization’s people have been cursed. They either turned into hilichurls or husk knights. Dainslief got a different curse, an immortality one, letting him keep his human form. How did his father avoid it, and does he also have one? However, those are questions to ponder for another day.
