Its speculated that all witchers infact may be immortal thanks to their mutations.
But its never been put to the test and most of them die at a middle age by being killed due to their profession or just the world they live in (might be discriminated against and a mob may rise up to try to kill one)
After all the things that live longer than all of them, elves, sorcerers/esses are the monsters, the kayren was ancient and thats what witchers are infused with and continue to mutate themselves with as they kill more monsters, take their parts and brew them and consume them to mutate more.
Paul_cz: Yeah Adda was 14, while Foltest was around 35, so he had her when he was 21. In TW2 he looks over 50 I'd say.
But when Saga ends, how old is Ciri? 16-17 I think ? And was she born after or before the Adda curse short story? I don't remember. If she was born after this story, then it would not make sense that Dandelion is so young, yeah.
Does he? I think he always constantly looks quite young 25-35.
Its the hair thats throwing you off.